The word repent is an unfortunate word choice in English for the meaning of the Hebrew נחם when it is associated with the Lord. I would argue that a better translation—when dealing with the Lord—would be to change His mind / or course of action. It is not the changing of the mind of a fickle person, but rather the Lord is always ready to show mercy to those who repent (שׁוב) and turn their ways.
The Lord through His prophets provides warnings that certain paths will lead to negative consequences. If we make a path correction, if we turn the right way, we can avert these consequences. On the way to work I saw a sign that caught my attention: “Turn to Jesus.” Well said! So it is that in Jeremiah we read: “If that nation, against whom I have pronounced [spoken against in warning], turn [וְשָׁב and turn, שׁוב] from their evil, I will repent [וְנִחַמְתִּי and I will change my mind / course, from נחם] of the evil that I thought to do unto them” (Jeremiah 18:8). The meaning of Jeremiah 18:8 is clear: “If that nation, against whom I have warned turn and repent from their evil, I will change my mind / course from the punishment I had prepared for them—had they not turned.”
CEV, and ERV correctly have used the very same terminology I have suggested, “change my mind.” As does the ISV, “But if that nation about which I spoke turns from its evil way, I’ll change my mind about the disaster that I had planned for it.” In Jeremiah 15:6b the Lord says, “I am weary with repenting.” At our slightest show of repentance the Lord blesses us and forgives us. After all, He taught us to forgive 70 times 7. He is the master forgiver.
But in this verse it is clear that the Lord’s patience will not last forever. In Ezekiel 24:14, we read “I the LORD have spoken it: it shall come to pass, and I will do it; I will not go back, neither will I spare, neither will I repent [i.e., neither will I change my mind]…” Why? Because the Lord, who can see the future as well as the past, knows that in this instance there will be no coming repentance.
This is precisely, also, what the expression and will not call back his words means in Isaiah 31:2a. That while the Lord will change his mind / course of action and is ever forgiving, there are some limits. People cannot just say, “I will repent later.” The Prophet Joseph Smith taught: “We should take warning and not wait for the death-bed to repent; as we see the infant taken away by death, so may the youth and middle aged, as well as the infant be suddenly called into eternity. Let this, then, prove as a warning to all not to procrastinate repentance, or wait till a death-bed, for it is the will of God that man should repent and serve Him in health, and in the strength and power of his mind, in order to secure His blessing, and not wait until he is called to die.”
In the Book of Mormon we read: “For behold, this life is the time for men to prepare to meet God; yea, behold the day of this life is the day for men to perform their labors. And now, as I said unto you before, as ye have had so many witnesses, therefore, I beseech of you that ye do not procrastinate the day of your repentance until the end; for after this day of life, which is given us to prepare for eternity, behold, if we do not improve our time while in this life, then cometh the night of darkness wherein there can be no labor performed” (Alma 34:32-33).
Let us always remember this invitation to come unto Christ and turn our hearts and our lives to Him: “Therefore also now, saith the LORD, turn ye even to me with all your heart, and with fasting, and with weeping, and with mourning: And rend your heart, and not your garments, and turn unto the LORD your God: for he is gracious and merciful, slow to anger, and of great kindness, and repenteth him of the evil” (Joel 2:12-13).