Albert Barnes on Acts 17:31

Because he hath appointed a day. This is given as a reason why God commands men to repent. They must be judged; and if they are not penitent and pardoned, they must be condemned. Rom 2:16.

Whom he hath ordained. Or whom he has constituted or appointed as judge. Acts 10:42. Jn 5:25.

Hath given assurance Has afforded evidence of this. That evidence consists,

(1.) in the fact that Jesus declared that he would judge the nations, Jn 5:25,26 Mt 25, and

(2.) God confirmed the truth of his declaration by raising him from the dead, or gave his sanction to what the Lord Jesus had said, for God would not work a miracle in favour of an imposter.

(g) "a day" Rom 2:16 (*) "ordained" "Appointed" (1) "given assurance" "offered faith"