The act of holding someone's hand means the person loves and will protect the one he is holding hands with. Graff does not love Ender, and he has no intention of protecting him. Graff wants to take a sweet little boy and turn him into a manipulating, vicious little monster. This little monster is supposed to save mankind from the evil buggers. Instead of protecting Ender, Graff will expose him to isolation, loneliness, and hate to see if Ender can take it and thrive. Hand-holding is also a symbol of trust, and Graff is not one to be trusted.
As for Graff blaspheming God, I didn't find a reference to that in the book. I did see Ender sending embarrassing messages over the desk system about Bernard, a bully who made people miserable. Ender says, "Cover your butts, Bernard is watching" and signed it God. Bernard had made a public snide comment about Shem twitching his butt when he walked. Of course God would send no such messages, but it made Bernard, who wanted to be the god of the Launchers, quit his persecution.