2 Peter 3:9

We are here told that the Lord is not slack - he does not delay beyond the appointed time; as God kept the time that he had appointed for the delivering of Israel out of Egypt, to a day (Exo 12:41), so he will keep to the time appointed in coming to judge the world. What a difference is there between the account which God makes and that which men make! Good men are apt to think God stays beyond the appointed time, that is, the time which they have set for their own and the church's deliverance; but they set one time and God sets another, and he will not fail to keep the day which he has appointed. Ungodly men dare charge a culpable slackness upon God, as if he had slipped the time, and laid aside the thoughts of coming. But the apostle assures us, I. That what men count slackness is truly long-suffering, and that to us-ward; it is giving more time to his own people, whom he has chosen before the foundation of the world, many of whom are not as yet converted; and those who are in a state of grace and favour with God are to advance in knowledge and holiness, and in the exercise of faith and patience, to abound in good works, doing and suffering what they are called to, that they may bring glory to God, and improve in a meetness for heaven; for God is not willing that any…

— Matthew Henry's Concise Commentary (public domain)

slack--slow, tardy, late; exceeding the due time, as though that time were already come. Heb 10:37, "will not tarry." his promise--which the scoffers cavil at. Pe2 3:4, "Where is the promise?" It shall be surely fulfilled "according to His promise" (Pe2 3:13). some--the "scoffers." count--His promise to be the result of "slackness" (tardiness). long-suffering--waiting until the full number of those appointed to "salvation" (Pe2 3:15) shall be completed. to us-ward--The oldest manuscripts, Vulgate, Syriac, &c., read, "towards YOU." any--not desiring that any, yea, even that the scoffers, should perish, which would be the result if He did not give space for repentance. come--go and be received to repentance: the Greek implies there is room for their being received to repentance (compare Greek, Mar 2:2; Joh 8:37).

— Jamieson-Fausset-Brown Commentary (public domain)