Jesus 

When speaking of the gifts of God it is easy to fall into the mentality of focusing only on the temporal or transitory. But the greatest gift of God is God Himself. And this is offered to us in and through the gift of Jesus.

The fundamental teaching of Christianity is that in His incarnation, Jesus takes on a human nature, healing what He assumes (to make positive the assertion of Saint Gregory Nanzianzus), thereby restoring our fallen nature. But this is at the service of the greater mystery of reunion with God Himself; it isn’t just Jesus making our current life more pleasant, but of reuniting us back to Himself. In his very person, he unites the human and divine, and it is precisely though this mystery that our human nature is also united with the divine as we participate in his life.

There can be no greater gift.