Ramban

KNOW THEREFORE from the [circumstances of the] departure from Egypt THAT THE ETERNAL THY G-D, HE IS G-D Who created heaven and earth, as I have explained. And know furthermore from this that He is THE FAITHFUL G-D Whose word shall not return void, and WHO KEEPETH THE COVENANT AND MERCY WITH THEM THAT LOVE HIM, AND KEEP HIS COMMANDMENTS, who fear His Name, TO A THOUSAND GENERATIONS of their seed, just as He kept for you the covenant of your fathers. And know further that He repayeth them that hate Him the recompense of their wickedness to the face of each one of them to destroy them, just as He destroyed the Egyptians and did not delay [in bringing punishment] to them. Now this attribute that he mentioned is true forever. Thus although there is a wicked man that prolongeth his life in his evil-doing, it happens to him only because of this above-mentioned attribute that He is the Keeper of Mercy, and he [the wicked] has done some good which must be recompensed. If so, there are among the attributes of the Holy One, blessed be He, but two ways [of dealing with people]: He repays good for good, and evil for evil. It is possible that those that hate Him [mentioned here as destined to be destroyed without delay] are those confirmed sinners who deny His existence and have no merit at all. As the Rabbis have said: “Rabbi Yashiyah said: Because of three things the Holy One, blessed be He, is long-suffering to the wicked in this world: they may repent, or they have observed commandments for which the Holy One, blessed be He, repays them their recompense in this world, or perhaps righteous people will descend from them. For so we find that He was long-suffering with Ahaz, and Hezekiah came from him; so also to Amon,, 21:19-22. and Josiah came from him; and so also to Shimei, and Mordecai came from him.” Thus all these [three above categories] are not included in [the term] those that hate Him. Now there is a secret in the expression ‘el panav’ (to his face) [And He repayeth ‘them’ that hate Him ‘el panav’ — “to his face”]], why does it change to the singular [to ‘his’ face, to destroy ‘him’]? Ramban alludes to the secret of the transmigration of the soul, so that at some future generation the recompense is still to “the face” of the sinner after he has been rewarded for the good he has done (Abusaula). as applying to a wicked man who has a good [i.e., a happy and prosperous] life. And then he returns to say, Thou shalt therefore keep the commandment etc., meaning: “therefore keep the commandment, and the statutes, and the ordinances so that you should not be among those who hate Him, who are destroyed, but instead you should be of those that love Him and keep His commandments who are remembered for good and for life.” Eikev