Or HaChaim on Genesis 27:23/אור החיים על בראשית כ״ז:כ״ג

1 ולא הכירו כי היו ידיו כידי עשו, he did not recognise him since his hands were like those of Esau. Isaac rejected the doubt created by Jacob's voice since a person can change his voice or the listener may mistake a voice for that of someone else, whereas he cannot change the hairs on his hands, a very distinctive mark of identification.

2ויברכהו, he blessed him. Before Isaac touched Jacob and established that he was Esau nothing had contradicted his impression that it was Jacob's voice he heard and that therefore he was faced by a swindler. Isaac had begun to think along the lines Jacob had been afraid of, i.e. that the swindler deserved to be cursed. Even though Isaac had not yet thought that far, he did begin to hate the person who he thought was trying to swindle him. The Talmud reports in Baba Metzia 84 that when the righteous are looking at someone with displeasure this brings a curse in its wake. [Rabbi Yochanan's displeaure at Rabbi Shimon ben Lakish's remarks resulted in the latter dying. Ed.] The Torah reports Isaac as blessing Jacob as a result of feeling his hands to teach us that he reversed his erstwhile intentions.