Genesis 15: 16: But in the fourth generation they shall come hither again: for the iniquity of the Amorites is not yet full.
God promised to Abraham that his seed would take possession of Canaan, but before that could happen, a specific amount of time had to elapse first in order that the cup of the Amorites’ iniquity could be filled up and overflow; in other words, Judgment Day for the Amorites was coming! Not only was God waiting for the sins of the Amorites to reach the brim of the cup, but He was going to use Israel as the instrument of judgment upon the Amorites when they went in to possess the land under the leadership of Joshua. Joshua was the destroying angel used by God to wipe out the Amorites and the other kingdoms that were squatting in the land of promise.
Because God is just, He did not preemptively judge the Amorites and the other kingdoms of Canaan, but patiently waited for them to earn the judgment He would bring upon them using Israel when they came in to claim the land of Canaan as their own (Joshua 24: 8: And I brought you into the land of the Amorites, which dwelt on the other side Jordan; and they fought with you: and I gave them into your hand, that ye might possess their land; and I destroyed them from before you.), thus the conquest of Canaan served the dual purpose of punishing the Amorites for their sin and giving the Israelites a land of their own. This purposeful delay served as an expression of God’s mercy, longsuffering, and patience toward sinful man, allowing the wicked kingdoms of Canaan to see their sin and repent of it. The Amorites were given a chance at repentance and salvation in much the same way as the Assyrians of Nineveh were given the same opportunity in the time of Jonah.
Fast-forwarding the clock into the twenty-first century, and we find out that the cup of the iniquity of the Gentiles has reached the brim and is spilling over. God has given the Gentiles two-thousand years under a Dispensation of Grace to amend their ways through repentance and salvation, but they have refused to do so, choosing instead to pursue sins of even greater magnitude than what was witnessed at any other time in history. But Judgment Day is coming for the Gentiles! God has seven vials filled up with the plagues of His wrath (Revelation 16) to pour out upon unrepentant sinners before He burns up the world with fire. Yes, the Gentiles are filling up their cup with iniquitous sin, but they shall surely be forced to drink of the cup that God shall give them, a cup filled to its brim with God’s furious wrath! (Revelation 14: 9 – 10: And the third angel followed them, saying with a loud voice, If any man worship the beast and his image, and receive his mark in his forehead, or in his hand, The same shall drink of the wine of the wrath of God, which is poured out without mixture into the cup of his indignation; and he shall be tormented with fire and brimstone in the presence of the holy angels, and in the presence of the Lamb:).