The Bible describes in various ways the reason for the ‘incarnation’, that is, the Son of God taking on human form. In this verse Jesus Himself says that He came so that people might possess abundant life.
Jesus was speaking to representatives of His own nation, the Jews. They were very familiar with the activity of shepherds and the hazards their sheep faced, not only from marauding animals but also from thieves and uncaring hired workers. They should also have been familiar with the way God likened people to sheep and Himself to their Shepherd, as this analogy was used in their sacred writings, our Old Testament (e.g. Isaiah 53:5; Psalm 23:1).
On this occasion Jesus extended the use of those figures of speech. He compared the nation’s religious leaders to thieves: they had robbed the people of their freedom by burdening them with numerous man-made religious rules. Against such a background Jesus announced that, in complete contrast, He had come to bring people fullness of life.
What credentials did Jesus have to make such a high claim? Essentially, there were two: Who He was and what He was soon to do. There are many references in John’s Gospel to Jesus’ claim to be God; one of the clearest is in chapter 10 verse 30, where Jesus said: ‘I and the Father are One.’ Then, in the verse (11) following the one we are considering, Jesus described Himself as the Good Shepherd Who ‘[lays] down His life for the sheep.’
Because He is both God and man, Jesus Christ alone was able to pay the price demanded by human sin. This He did when, on a cross outside Jerusalem, He yielded up His life as a sacrifice. Having risen from the dead the third day, He now offers forgiveness and eternal life (Romans 6:23) as a gift to repentant sinners. This is the only real life: life enjoyed in fellowship with God, truly abundant life.
(Quotations from the ESV)