2 Therefore it was that He forbade Mary to touch Him, and said to her, “Touch me not; for I am not yet ascended unto the Father.” What is this? He gave Himself to be handled by the disciples, and did He shun Mary's touch? Is not He the same that said to the doubting disciple, “Reach hither your fingers, and feel the scars”? Was He at that time ascended to the Father? Then why does He forbid Mary, and says, “Touch me not; for I am not yet ascended to the Father?” Or are we to say, that He feared not to be touched by men, and feared to be touched by women?
The touch of Him cleanses all flesh. To whom He willed first to be manifested, by them feared He to be handled? Was not His resurrection announced by women to the men, that so the serpent should by a sort of counterplot be overcome? For because he first by the woman announced death to man, therefore to men was also life announced by a woman. Then why was He unwilling to be touched, but because He would have it to be understood of that spiritual touch? The spiritual touch takes place from a pure heart.
That person does of a pure heart reach Christ with his touch who understands Him coequal with the Father. But whoso does not yet understand Christ's Godhead, that person reaches but unto the flesh, reaches not unto the Godhead. Now what great matter is it, to reach only unto that which the persecutors reached unto, who crucified Him? But that is the great thing, to understand the Word God with God, in the beginning, by whom all things were made: such as He would have Himself to be known when He said to Philip, “Am I so long time with you, and have you not known me, Philip? He that sees me, sees also the Father.”
Source: Homilies on the First Epistle of John (New Advent)