The biblical answer to this perennial question is union with Christ, which the 13th century Franciscan theologian Bonaventure beautifully articulates in his spiritual meditation, The Tree of Life.
It is true that the end of all desires is happiness, which is “a perfect state with the presence of all goods.” No one reaches this state except by an ultimate union with him who is the fountain and origin of goods that are both natural and gratuitous, both bodily and spiritual, both temporal and eternal. And this is the one who said of himself: “I am the Alpha and the Omega, the beginning and the end” (Apoc. 1:8). As all things are produced through the Word eternally spoken, so all things are restored, advanced and completed through the Word united to flesh. Therefore he is truly and properly called Jesus, because there is no other name under heaven given to men by which one can obtain salvation (Acts 4:12).
Believing, hoping and loving
with my whole heart, with my whole mind
and with my whole strength,
may I be carried
to you, beloved Jesus,
as to the goal of all things,
because you alone are sufficient,
you alone are good and pleasing
to those who seek you and love your name.
For you, my good Jesus,
are the redeemer of the lost,
the savior of the redeemed,
the hope of exiles,
the strength of laborers,
the sweet solace of anguished spirits,
the crown and imperial dignity of the triumphant,
the unique reward and joy of all the citizens of heaven,
the renowned offspring of the supreme God
and the sublime fruit of the virginal womb,
the abundant fountain of all graces,
of whose fulness we have all received.
 Boethius, The Consolation of Philosophy, Book III.2.
 Matt. 22:37; Mark 12:30; Luke 10:27.
 Ps. 5:12.
 John 1:16
In the third book of The Institutes of Christian Religion, the 16th century Reformer John Calvin also insisted that union with Christ is the telos of human life, which shows that Protestants and Catholics both affirm this essential doctrine:
- Desiring God 2014 Conference for Pastors: John Piper, Glorifying God by Bearing Fruit in Union with Christ; Michael Horton, Calvin on Union with Christ; Sinclair Ferguson, Union with Christ: Mind-Renewing Foundations and Union with Christ: Life-Transforming Implications
- Modern Reformation: J. V. Fesko, A More Perfect Union? Justification and Union with Christ
- Ligonier: Philip Ryken, Union with Christ: A Matter of Spiritual Life and Death
- Themelios: J. V. Fesko, John Owen on Union with Christ and Justification
- Modern Reformation: Michael Horton, Union with Christ
- J. Todd Billings, Union with Christ: Reframing Theology and Ministry for the Church (see The Gospel Coalition review and interview)