For I have come down from heaven not to do my will but to do the will of him who sent me. And this is the will of him who sent me, that I shall lose none of all those he has given me, but raise them up at the last day. For my Father’s will is that everyone who looks to the Son and believes in him shall have eternal life, and I will raise them up at the last day.”
Here is the basis for irresistible grace and the final preservation of the saints. The Father's will and the Son's accomplishments. Nothing to do with the works of the elect.
These verses emphasize the divine sovereignty in salvation; it is God's will that is not forestalled by any failure in the accomplishment of Jesus. But John does not shy away from human responsibility; it is our duty to look to Jesus and believe in him.
Who are those who have been give to Jesus? In the first instance it is the disciples - though not even all of these; one was from the beginning the son of perdition. But there are other 'sheep who are not of this fold' (chapter 10). But there will be others everyone who looks to the Son and believes in him shall have eternal life.
This eternal life is more than just everlasting existence - it is a real resurrection life having been 'dead in trespasses and sins' we are no 'alive in him'; a transformed nature of being part of God's family; we do not have the fulfilment but we have the foretaste.