Why did Allah Almighty say in the verse of repentance: "And Allah was Knowing and Wise" and not "Oft-Forgiving, Most Merciful," and why did He mention "evil" in one place and "sins" in another?

The attributes of repentance and mercy are mentioned in the verse preceding the second verse to avoid repetition. The attributes of knowledge and wisdom are suitable for the subsequent verse, for God is All-Knowing of the sincere and All-Wise in not punishing the penitent. The difference in wording between "evil" (السوء) and "evil deeds" (السيئات) in the two verses might be for rhetorical variation, or "evil" (السوء) might refer to disbelief and sins, while "evil deeds" (السيئات) refer to sins lesser than disbelief, although "evil deed" (السيئة) can also be applied to disbelief.