13 Moreover, when you have been deemed worthy of the grace, He then gives you strength to wrestle against the adverse powers. For as after His Baptism He was tempted forty days (not that He was unable to gain the victory before, but because He wished to do all things in due order and succession), so thou likewise, though not daring before your baptism to wrestle with the adversaries, yet after you have received the grace and art henceforth confident in the armour of righteousness, must then do battle, and preach the Gospel, if you will.
Source: Catechetical Lectures (New Advent)