John Calvin Commentary John 20:14

"When she had thus said, she turned herself back, and beholdeth Jesus standing, and knew not that it was Jesus." — John 20:14 (ASV)

And seeth Jesus standing. It may be asked, from where did this mistake arise, that Mary does not recognize Jesus, with whom she must have been intimately acquainted? Some think that He appeared in a different form, but I think that the fault rather lay in the eyes of the women. As Luke (Luke 24:16) says of the two disciples, their eyes were withheld from knowing him. We will not say, therefore, that Christ was continually assuming new shapes, like Proteus, but rather that it is in the power of God, who gave eyes to men, to lessen their sharpness of vision whenever He sees fit, so that seeing they may not see.

In Mary we have an example of the mistakes into which the human mind frequently falls. Though Christ presents Himself to our view, yet we imagine that He assumes various shapes, so that our senses conceive of anything rather than the true Christ; for not only are our powers of understanding liable to be deceived, but they are also bewitched by the world and by Satan, so that they have no perception of the truth.