Charles Ellicott Commentary Matthew 12:13

"Then saith he to the man, Stretch forth thy hand. And he stretched it forth; and it was restored whole, as the other." — Matthew 12:13 (ASV)

Then he said to the man — Mark, with his usual vividness, adds the look, gesture, and feeling that accompanied the words: looking around at them with anger, being grieved at the hardness of their hearts.

It was restored whole — that is, as the tense implies, in the very act of stretching his hand out. The man’s ready obedience to the command—which would have seemed like an idle mockery if he had not believed in Jesus’s power—was, by that very act, proof that he had faith to be healed.