The church at Colosse was under constant pressure from teachers of many religious philosophies, pagan religions and corruptions of Christianity that were around in the early days of the church - not so very different from today!  Paul prayed that they might have the strength to resist all the pressure.  He prayed they'd have the power to work out what was true and not true and to stick to their guns and follow what they had been taught about Christ and their salvation. It was important that they display the joy of knowing the Lord as that would make a great witness to the people around them - as it always does when Christians face adversity with joy and praise to God.

New Bible Commentary p 1265.  Being strengthened with all power (NIV) indicates how they are to live in a way that is worthy of teh Lord.  The standards set before the Colossians are high, far higher than those of teh false teachers, and it might seem they could not be achieved.  But this is not the case.  Paul heaps up terms of power and strength to stress that: nothing short of God's almighty power at work within them will enable them to live in a way that is pleasing to him;  his glorious might is more than adequate for the Colossians' needs;  and this strength will be given to them day by day as they confront varying situations (the present tense being strengthened suggests the ongoing strengthening by God.).  The outworking of his divine power is not in spectacular miracles but is for great endurance and patience (NIV), particularly in the face of opposition.  By enduring patiently as they suffer, Christians show that they have their hope set on God.

In everyday living, we need power to endure and power to enable us to give thanks, whatever happens to us, - to be able to see God's hand in everything in our lives, even if it's not comfortable or enjoyable for us.

V 12.
and to give thanks to the Father who has made you fit to share the heritage of God's people in the realm of light
NIV.  giving thanks to the Father, who has qualified you to share in the inheritance of the saints in the kingdom of light.
NLT. ...always thanking the Father, who has enabled you to share the inheritance that belongs to God's holy people, who live in the light.
The Message: ...thanking the Father who makes us strong enough to take part in everything bright and beautiful that he has for us.

When we learn to trust God and rely on him we begin to take advantage of the power he offers us.  Through our relationship with him, made possible by Christ, we share with Christians through the ages freedom from guilt and worry. And we know we have inherited with Christ the title of Children of God and a place in the kingdom of God.  Paul considered that giving thanks was a very important outcome of faith.  In Colossians 2: 7,  he wrote: Be rooted in him; be consolidated in the faith you were taught, let your hearts overflow with thankfulness.  In 1 Thessalonians 16 - 18,  he wrote: Be always joyful; pray continually; give thanks whatever happens; for this is what God in Christ wills for you.  In Ephesians 5: 20, we read: ..and in the name of our Lord Jesus Christ give thanks every day for everything to our God and Father.

New Bible Commentary p 1265.  Paul prays that the Colossians will joyfully give thanks to the Father (NIV) for this pleases him in every way.  'Thanksgiving' in Paul's letters refers to a thankful attitude of mind which is expressed outwardly and often publicly.  By us mentioning what God has graciously done in his Son, other Christinas are encouraged to praise him also; and as thanksgivings increase so God is glorified.  Joyful thanksgiving is an activity Christians should regularly engage in.  There are good grounds for doing so.  In fact, the regular offering of thanks to the Father is a mark of a true Christian.
                                                    The Almighty One has acted on their behalf and already fitted them for an eternal inheritance.  This language is full of Old Testament echoes and recalls the promise first given to Abram (Genesis 13: 14 - 17) which was later renewed to Israel (Numbers 26: 52 - 56).  The inheritance to which Paul refers belongs to a higher plane and a more lasting order than the land of Canaan, for it is in the kingdom of light, ie in the realm of the light of the age to come, in heaven itself.  It belongs to a spiritual dimension, unable to be ravaged by war, famine or the like.  this inheritance is the 'hope laid up in heaven' (mentioned in Col. 1: 5 and Col. 3: 1-4) and is none other than the Lord Jesus himself.

V 13, 14
He rescued us from the domain of darkness and brought us away into the kingdom of his dear Son, in whom our release is secured and our sins forgiven.
NLT. For he has rescued us from the one who rules in the kingdom of darkness, and he has brought us into the Kingdom of his dear Son.  God has purchased our freedom with his blood and has forgiven all our sins.
The Message.  God rescued us from dead-end alleys and dark dungeons.  He's set us up in the kingdom of the Son he loves so much, the Son who got us out of the pit we were in, got rid of the sins we were doomed to keep repeating.

Here it is - the 'good news' again.  Paul always comes back to it - what God has done for each one of us through the sacrifice of Christ.  Like Paul, we must never forget it, and always be ready to tell others the reasons for our freedom and joy in life.

Quest Study Bible note, p 1627.  The kingdom of darkness.  The influence and destructive power Satan and sin have over the world, broken only through the authority of Christ.  Christians occasionally can fall prey to the darkness, but they don't have to.  In Christ we have the resources to overcome Satan.

V 15 - 17
He is the image of the invisible God; his is the primacy over all created things.  In him everything in heaven and earth was created, not only things visible but also the invisible orders of thrones, sovereignties, authorities and powers: the whole universe has been created through him and for him.  And he exists before eveything, and all things are held together in him.
NIV.  He is the image of the invisible God, the firstborn over all creation.  For by him all things were created: things in heaven and on earth, visible and invisible, whether thrones or powers or rulers or authorities; all things were created by him and for him.  He is before all things, and in him all things hold together.
TEV.  Christ is the visible likeness of the invisible God.  He is the first-born Son, superior to all created things.  For by him God created everything in heaven and on earth, the seen and the unseen things, including spiritual powers, lords, rulers, and authorities.  God created the whole universe through him and for him.  He existed before all things, and in union with him all things have their proper place.

This passage make is very clear that Jesus is supreme in creation.  If we are to take this seriously, we cannot possibly think that Jesus was just a 'good man' or a 'great teacher' or simply a 'prophet' and nothing more.  This passage stirs me to worship him!
Jesus - God in human form,  shows us God in a way we can understand.  It took me many years of loving God and loving Jesus as I read and heard about him, to realise that Jesus is God and has all the power of God.  And the realisation blew my mind!!!
Jesus - God the Son - was at creation and was instrumental in the creation of the whole universe - all that we know and what we don't yet know!  He has absolute power over all of creation.  He was there at the beginning and will be there at the end. Jesus Christ is Lord!

 Hebrews 1: 1 - 4 (NIV) says something very similar: In the past God spoke to our forefathers through the prophets at many times and in various ways, but in these last days he has spoken to us by his Son, whom he appointed heir of all things, and through whom he made the universe.  The Son is the radiance of God's glory and the exact representation of his being, sustaining all things by his powerful word.  After he had provided purification for sins, he sat down at the right hand of the Majesty in heaven.  So he became as much superior to the angels as the name he has inherited is superior to theirs.

Quest Study Bible note p 1627.  Paul borrowed this term (firstborn) from his Jewish upbringing: firstborn was a Hebrew way of saying someone was especially honoured.  The nation of Israel was called firstborn (Exodus 4: 22), as was David (Psalm 89: 27).  The word didn't refer to their physical birth but to their place of honour before God.  So Paul is saying that Christ has a place of honour over all creation.

V 18
He is, moreover, the head of the body, the church.  He is its origin, the first to return from the dead, to be in all things alone supreme.
TEV.  He is the head of his body, the church; he is the source of the body's life; he is the first-born Son who was raised from death, in order that he alone might have the first place in all things.

Paul pictures the church as Christ's body on earth, with Christ as the head.  If we think of that picture as that of a physical body, the head is where the planning, the thinking, the decision-making happens.,  The head is the means of communication.  Through the eyes in our head we receive visual information and we hear sound through our ears.  Without the sensory organs in our head and the brain that nestles inside it, we'd be pretty useless.  And the church is useless without Christ.  If we think of the body as a corporate organisation, then Christ must be the CEO (or whoever in the organisation has the ultimate power - my knowledge of corporate structures is a bit limited!).  In any terms, Christ is the absolute head - the person in charge of the church.  (And the church is not an institution or an organisation - the church is the people who are Christians and who jointly undertake God's work here on earth, as well as all those who have done so in the past.)

New Bible Commentary, p.1267.  With the words he is the head of the body, the church, the centrality of christ in relation to his people is stressed.  His headship points to a close personal and living relationship with them in which he rules over his people in the way that the head of a body exercises influence over its various parts.  Headship also refers to their total dependance on him for life and power.  Church is not some universal congregation, scattered throughout the world, to which all believers belong, but a heavenly assembly, gathered around Christ.  Even as they go about their ordinary daily tasks, all Christians are members of this gathering in heaven, because of their fellowship with him.  Christ is the beginning in the sense that he is the firstborn from among the dead, ie the founder of a new humanity.  The resurrection age has burst forth......

V 19.
For in him the complete being of God, by God's own choice, came to dwell.
NLT. For God in all his fullness was pleased to live in Christ.
TEV.  For it was by God's own decision that the Son has in himself the full nature of God.

It was God's choice to come to earth in the form of a human being - Jesus. Jesus was completely human in every way, with human limitations, but he was also God, with all the characteristics of God - his wisdom, love, authority and power. He was the complete person of God - with all the characteristics of  the creator: designer, builder, owner, maintainer, redeemer.

V 20.
Through him God chose to reconcile the whole universe to himself, making peace through the shedding of his blood on the cross -- to reconcile all things, whether on earth or in heaven, through him alone.
TEV.  Through the Son, then, God decided to bring the whole universe back to himself.  God made peace through his Son's death on the cross, and so brought back to himself all things, both on earth and in heaven.

God created the whole universe to be in complete harmony with him, but human beings have gone their own way and have tried to shut God out of their lives.  The harmonious relationship that God planned was broken becaue he allowed humanity free choice - and humanity chose to go its own way.  The story of Adam and Eve and the Fall  (Genesis 2) is a way of expressing that rift in people's relationship with God and its implications for the whole of creation.  In Jesus Christ,  his death on the cross and subsequent resurrection, God has put into operation his plan for getting things back to the way he originally wanted between himself and human beings who choose to accept his forgiveness and beleive in Jesus Christ as their Lord and Saviour.