"The Bible says ‘God repented.’
Doesn’t that show He is capable of sin?"
means "to have a change of mind." When the
Bible tells sinners to repent, it means to change their
direction, to turn from their sins. God’s "repenting"
is when He turns away from His fierce anger toward sinners.
He warns men of the consequences of their disobedience.
If they repent (turn from their sins), He will "repent"
by not pouring out His promised wrath on them. For instance,
Jonah 3:8,9 says, "Let them turn every one from
his evil way...Who can tell if God will turn and repent,
and turn away from his fierce anger, that we perish
not?" (See also Jeremiah 18:8.)