This parable was told by Jesus in response to a question by the disciples about the  'end of the age'
(Matthew 24: 3)....

The Greek word parousia, meaning 'coming', was used mainly for formal visits by those in authority. In the New Testament it usually, but not always, refers to Jesus' predicted second coming. (New Bible Commentary. p.936)

The only thing which may be said with conviction about the time of the parousia is that it will come when it is not expected. (New Bible Commentary. p 937)

From Drane J. Introducing the New Testament……

p 190. Matthew has a number of parables on the subject of the second coming and last judgement that are not found in the other Gospels. Most of them are concerned to encourage Christians to live in a state of constant readiness for Jesus' return, because "you do not know the day or the hour". Perhaps some members of Matthew's church were beginning to doubt that Jesus would return; parables like that of the ten bridesmaids emphasise that with such an attitude Christians can never be in a fit state to meet their Lord.

p. 192. (Matthew's) Gospel can be dated either in the period AD 80-100 (with the majority of scholars), or pre AD 70, perhaps as early as AD 40-60 (with Robinson, Guthrie and one or two German writers).

Vs 1-4.
'When that day comes, the kingdom of Heaven will be like this. There were ten girls, who took their lamps and went out to meet the bridegroom. Five of them were foolish, and five prudent; when the foolish ones took their lamps, they took no oil with them, but the others took flasks of oil with their lamps'
Preparing to meet the Bridegroom.  All bridesmaids went out to meet him; all took lamps.  None knew exactly when he was coming.  Some were prudent and took extra supplies of oil, in case he was a long time.  Others assumed he'd come soon and were not prepared for a long wait - they didn't think ahead.

**We don't know when Jesus is coming again, but we must be prepared for him to come at any time.

Vs 5.
'As the bridegroom was late in coming they all dozed off to sleep.'
They all went to sleep while they waited - he took so long.

** We should live our lives normally while we wait, following our usual routines with times of alertness and busyness and times of rest.

Vs 6 - 13.
'But at midnight a cry was heard: "Here is the bridegroom!  Come out to meet him."  With that the girls all got up and trimmed their lamps.  The foolish said to the prudent, "Our lamps are going out; give us some of your oil."  "No," they said; "there will never be enough for all of us.  You had better go to the shop and buy some for yourselves."  While they were away the bridegroom arrived; those who were ready went in with him to the wedding; and the door was shut.  and then the other five came back.  "Sir, sir," they cried, "open the door for us."  But he answered, "I declare, I do not know you."  Keep awake then; for you never know the day or the hour.'
The bridegroom arrived at midnight while they were still asleep - at an unexpected time and not the most convenient time.  The prudent bridesmaids were able to be up and quickly ready to meet him.  The foolish bridesmaids were out of oil and had to go out and buy more.  Where would they get extra oil at that inconvenient time? They risked being gone for too long searching for oil.
The groom arrives and the prudent bridesmaid all go back to his house with the bride while the foolish bridesmaids are off looking for more oil.  The door is locked and they are locked out of the festivities.

** A warning!  We need to be ready for God's timing and be prepared.  How? By making sure we keep in touch with him and build a close relationship so that when the time comes, he will recognise us as his own.  We need to make sure our life is lived in accordance with his will, so we are not distracted by things which take our attention away from him.  Otherwise, we risk missing out on all the good things he has prepared for us.