(Jesus, on the previous day had provided food for a crowd of 5000 men, not counting the women and children, from five barley loaves and two fish.  Then, with his disciples, he had gone across the sea of Galilee to the other side.)

Vs. 24, 25
When the people saw that neither Jesus nor his disciples were any longer there, they themselves went aboard these boats (from Tiberius) and made for Capernaum in search of Jesus.  They found him on the other side.  'Rabbi', they said, 'when did you come here?'

When they caught up with Jesus, they asked a fairly ordinary question, "How long have you been here?" - prattling, because they didn't know what to say?

v. 26
Jesus replied, 'In very truth I know that you have not come looking for me because you saw signs, but because you ate the bread and your hunger was satisfied...'

Jesus cuts to the heart of the matter.  He understands us completely - knows what we are really thinking and what are our true motives.  He confronted the people - "You haven't come looking for me because you understand who I am and what I'm here for; you came because I gave you food."  He then builds on that to teach them something.

v. 27
'...You must work, not for this perishable food, but for the food that lasts, the food of eternal life.
This food the Son of Man will give you, for he it is upon whom God the Father has set the seal of his authority.'

Jesus lets us know that God's gift of life is more important than anything we can earn by our own work or effort.
Son of Man - understood by the Jews as 'Messiah' and used by Jesus in referring to himself.  The term also emphasises Christ's humanity.
'It is he upon whom God has set his seal of authority' (NEB)  'Seal' = given to God's representative who has authority from God.  Jesus has that authority over creation: he is Lord.

v. 28
'Then what must we do,' they asked him,'if we are to work as God would have us work?'

They asked, "What do we have to do?" They picked up on the word 'work' - doing - thinking they had to do something to earn God's favour.  It is human nature to want to do it ourselves.  It's easier to think that we have to do something, to feel that we control things ourselves.
God's love is perfect.  Ours isn't - it's selfish (self-centred, 'cupboard love')  It's hard for us to understand that God wants to give, no strings attached!

v.29
Jesus replied, 'This is the work that God requires: believe in the one whom he has sent.'

Jesus tells them that the 'work' that God asks of us is to believe in the one God ha sent - that is, Jesus.  Trust in Jesus is all God asks of us - nothing we can do will please him more than faith in him.  Without that faith and trust, we are unable to accept his gift of eternal life.  We're too busy running around trying to earn it that we don't see him holding it out for us to grasp.

v.30
They said, 'What sign can you give us to see, so that we may believe in you?  What is the work you do?

They asked him for a miraculous sign to help them believe in him!!!! THESE ARE THE PEOPLE WHO SAW HIM TURN 5 LOAVES AND 2 FISH INTO ENOUGH FOOD TO ADEQUATELY FEED MORE THAN 5000 PEOPLE!!!!  And they're still asking for a miracle!

We wouldn't be so dense.......or would we?

v. 31
'Our ancestors had manna to eat in the desert; as scripture says, "He gave them bread from heaven to eat." '

They quoted to Jesus the sign that God had given Moses' people in the desert - sending bread from heaven when they had no food.  (!!!! short memories.  Where had the bread and fish come from on the previous day?)
How often do we forget what God has done for us, taking his good gifts for granted, because they come to us in ordinary ways, with no spectacular effects.

New Bible Commentary comments (p.1038) , 'they were probably thinking that the miracle that Jesus had performed was not as 'miraculous' as manna regularly appearing out of no-where every day.  They wanted Jesus to do something even better to prove he was greater than Moses.

The people were thinking of the Messiah as an earthly leader who would defeat the Romans and free them from Roman rule on earth as Moses had delivered the Israelites from Egypt.  They wanted Jesus to prove he could do what Moses did.

v. 32-35
Jesus answered, 'I tell you this: the truth is, not that Moses gave you the bread from heaven, but that my Father gives you the real bread from heaven.  The bread that God gives comes down from heaven and brings life to the world.'  They said to him, 'Sir, give us this bread now and always.'  Jesus said to them, 'I am the bread of life.  Whoever comes to me shall never be hungry, and whoever believes in me shall never be thirsty...'

Jesus knew what they were thinking.  He reminded them that it was God, not Moses, who delivered the Israelites from slavery and who provided them with food.  He told them again that God gives them the true bread - himself - that leads to eternal life.

It is not what we do, but who we trust that determines our eternal future.