In the last two verses of John 17, we find the final utterance of Jesus to His disciples before He suffered and died on the cross. I believe that these two verses are the climax of the entire purpose of the gospel. Here is part of the prayer that Jesus prayed.
O righteous Father! The world has not known You, but I have known You; and these [disciples] have known that You sent Me. And I have declared to them Your name. (John 17:25–26)
The name Jesus came to reveal was Father. You find very few uses of the word Father as a title of God in the Old Testament. The only person who could fully reveal the Father was the Son. Then, Jesus said,
I have declared to them Your name, and will declare it, that the love with which You loved Me may be in them, and I in them. (verse 26)
The ultimate purpose of the gospel is this love relationship with God by which God loves us in exactly the same way that He loved—and still loves—Jesus, and that we love God in exactly the same way that Jesus loves Him. That is the purpose—to bring us into the family of God, to bring us into a relationship with God as Father that is the same relationship that Jesus has. It enables us to love God with the same love with which Jesus loves Him. You cannot ask for more. It is unimaginable. It is past our human minds to conceive what it entails. But it is the goal, the ultimate purpose. Everything else is secondary.