What two pieces of evidence regarding his Christian nature are presented against Proctor?
The answer to your question is in Act Two. Hale goes to the Proctor home to tell them Rebecca Nurse has been charged with witchcraft and to warn the Proctors to get their religious lives in order. Rebecca's arrest shows how out of control the situation has become, since she is a respected, wealthy member of the community.
Hale questions why Proctor rarely attends church on Sunday, citing that Proctor has missed services "twenty-six time in seventeen month". Proctor defends himself, saying Elizabeth was sick, and he prayed at home when he couldn't go to church. Then Proctor admits his dislike for Parris, telling Hale about the golden candlesticks that Parris insisted the church have instead of the pewter ones the church had always had.
The second issue Hale brings up is that only two of Proctor's three sons have been baptized. Proctor answers Hale that "I like it not that Mr. Parris should lay his hand upon my baby. I see no light of God in that man. I'll not conceal it." It's ironic, however, that when Proctor is asked by Hale to cite the Ten Commandments, he forgets the one regarding adultery.
This scene also occurs just before Elizabeth is arrested for witchcraft.
In Act II, Hale comes to question the Proctors about their Christian character. At that time, Proctor is suspicious because he does not go to church regularly and he cannot say all the ten commandments. He ironically forgets the one prohibiting adultery.
In Act III, Proctor goes to the court with Mary Warren in an attempt to prove that Abigail is a liar. It backfires on him when Mary Warren turns against him in her fear, and accuses Proctor of being with the Devil. Proctor also screams out, "God is dead", out of his sheer frustration with the proceedings. During the Puritan time period where government and religion were one in the same, this would have been considered blasphemy and treason.