In Summa theologiae Ia IIae, q. 3, a. 8, St. Thomas Aquinas asks, "Whether man’s happiness consists in the vision of the divine essence?"
His answer: For perfect happiness, the intellect needs to reach the very Essence of the First Cause (i.e. God). Thomas' argument runs like this:
- Happiness consists in attaining the final good.
- The final good is the divine essence.
- Therefore, for perfect happiness the intellect needs to reach the very essence of the First Cause.
Our knowledge of God in this life is analogical.
It's worth noting that even the hesychast tradition in the Orthodox Church denies that mystics can see the Divine Essence in this life. Rather, they "see" the "Divine Energies" in this life (whatever that means).