The incarnation is an act of God's grace

The first thing to be said, is that the hypostatic union must be looked at only from the perspective of God’s amazing act of grace, in which God the Son freely descended into our human existence, and freely assumed human being into oneness with his divine being. That was an act of sheer grace. He did not need to do it. He did not owe it either to himself or to man to do it; it is an act grounded only in the pure overflowing love of God. It is in no sense a two-sided event, for even though there is within it, in the unity of divine and human natures, act of God and act of man, the whole act of incarnation, including all the divine and human acts within the hypostatic union, is grounded solely and entirely and exclusively in the act of God's grace.—T. F. Torrance, Incarnation: The Person and Life of Christ, 206