From Tom Schreiner's recent New Testament Theology:
“The purpose of life is to honor God, though again, John insists that God
cannot be honored if Jesus Christ is not honored (John 5:23). The purpose of
every life is to honor God in Christ, which fits, of course, with the major
thesis that I put forth in this book [“the centrality of God in Christ is the
foundational theme for the narrative unfolded in the NT”; p.119]. The Father is
glorified if people bear much fruit (John 15:8), and this fruit likely involves
both Christian character and the spread of the gospel so that others receive
eternal life (p.138).