This also accords with the circumstances in which these words were spoken to Moses. The holy prophet Moses asked the Lord God to deem him worthy of a great mercy, to see His face. The Lord told him that His face could not be seen.
Yet He said: this is what I will do for you. I will pass before you in My glory. Or, I will cause a visible manifestation of My glory to pass before your eyes, as a sign of My presence.
I will proclaim to you: the Lord is before you. And "I will have mercy on whom I have mercy, and I will show compassion to whom I show compassion" (cf. Ex 33:19). That is, to the words, "the Lord is before you," I will add these words also.
Thus the Lord promised, and He commanded Moses to ascend the mountain. When he had ascended, the promised manifestation of God's glory followed: "The Lord passed before his face and proclaimed: The Lord, the Lord God, compassionate and merciful, long-suffering, abundant in mercy, and true. He keeps righteousness and shows mercy, forgives the penitent, takes away iniquities, unrighteousness, and sins, and will not cleanse the guilty" (cf. Ex 34:6-7). That is, the one who is guilty and does not repent He will not acknowledge as clean, but will punish.
These words were spoken in place of: "I will have mercy on whom I have mercy, and I will show compassion to whom I show compassion." They serve as a fuller explanation of them, proceeding from the mouth of the Lord Himself.
The chief thought in these words is this: the Lord has mercy on the one worthy of mercy, and punishment will not pass by the unworthy. If we apply them to the question, is there unrighteousness with God because He chose Jacob and rejected Esau, we see the direct answer. No. He chose Jacob because Jacob ought to be chosen as worthy. He rejected Esau because Esau ought to be rejected as unworthy.
Let us add that the holy prophet Moses asked the Lord for the mercy of seeing His face after the Lord had refused to go with the people. Then, entreated by holy Moses, He again agreed to go with them.
This happened when the Israelites had cast the calf and began to worship it as God. Holy Moses was then on the mountain. The Lord said to him: the people have sinned and are worshiping the calf. I will destroy them all and produce a new people from you.
The prophet began to entreat the Lord not to do this. Otherwise, all would blaspheme Him, saying that He had brought the people out of the land of Egypt in order to destroy them in the wilderness. "Turn from the wrath of Thy anger, and be merciful concerning the wickedness of Thy people" (cf. Ex 32:12).
The Lord was propitiated and set aside that dread decree, though not the punishment. Holy Moses came down from the mountain, summoned those who still remained faithful to the Lord, and commanded them to slay the originators of the evil. They did this, and about three thousand men fell.
After this, holy Moses again ascended the mountain to the Lord and began to pray: "This people has sinned a great sin. And now, if Thou wilt forgive their sin, forgive it. But if not, blot me out of Thy book in which Thou hast written me."
The Lord said to Moses: "Whoever has sinned before Me, I will blot him out of My book." And He added: "In the day when I visit, I will bring their sin upon them." This shows that the Lord determined to punish the sinners in His own person.
Then it is written: "And the Lord struck the people because of the making of the calf" (cf. Ex 32:32, 35). Thus many more fell besides those three thousand. Many fell, but not all, though almost all had sinned.
Who made the choice? God's foreknowledge did. It saw those who could amend themselves and bring forth good fruits, and it spared them. It saw the unrepentant in heart and struck them.
Perhaps in the present case some of the former were more guilty than some of the latter. Oecumenius writes: "If there is no unrighteousness with God, and yet, when all worshiped the calf, God says, 'I will have mercy on whom I have mercy,' then certainly it is because He secretly entered men's hearts with His eyes and saw who was worthy of mercy and who was unworthy."
But even this did not appease the wrath of God. He declared to Moses: I will send an Angel with you, but I Myself will not go, lest I destroy you for your hardness of heart.
When the people heard this dread decree, they were deeply contrite. They took off their ornaments and clothed themselves in garments of mourning. And Moses began to entreat the Lord that He Himself would go with them.
The Lord was propitiated and said: "This word also I will do for you, for you have found grace before Me" (cf. Ex 33:17). After this holy Moses asked the Lord to show him His face. Then he heard the words of which we speak: "I will have mercy on whom I have mercy" (Ex 33:19).
If we compare these words with those which the Lord spoke when He refused to go with the people Himself, lest He destroy them all for their stiff-neckedness, we may also interpret them thus. I will indeed go with you. Though I will not destroy you all in case of some transgression, I will not leave the deed unpunished.
Whom to have mercy on and whom to punish, I will see then. I will have mercy on the one who will be worthy of mercy, and so forth.
Chrysostom puts these words into the mouth of the Lord: "It is not your business, Moses, to know who is worthy of love for mankind. Leave this to Me."
Thus the whole circumstance shows that the Lord both has mercy and punishes according to what each one deserves. This may be according to deeds already done, or according to their life foreseen in the future. This is precisely the meaning of the words: "I will have mercy on whom I have mercy," and so forth.
Ambrosiaster paraphrases the passage thus: "By mercy, He says, I will have mercy on the one on whom I take pity. That is, I will have mercy on the one whom I foresee will turn and remain faithful to Me. I will show My compassion to the one whom I foreknow will turn from error to Me with an upright heart. This means giving to the one to whom it should be given, and not giving to the one to whom it should not be given."
Oecumenius applies this to the course of the Apostle's argument and says: "God does not act unrighteously toward the present Jews. Even now those who are worthy are saved, because they believe, and those who are unworthy perish, because they do not believe. 'I will have mercy on whom I have mercy' means, as it were: I know who are worthy of salvation and who are unworthy. If Moses did not know who were worthy and who were unworthy, is it for us to know the causes of what takes place? Who shall search out the judgments of God?"
Thus here we may see a third example of how God receives some and rejects others. This one is already taken from within the assembly of the sons of Israel.
These words may also be explained thus: I have mercy on whom I will. The following thought agrees with this. Yet even if they are understood in this way, the basic thought remains one and the same. God has mercy on the worthy, just as He punishes the unworthy.
God always acts independently, as He wills. Yet He acts in accordance with His boundless righteousness, as also with His infinite mercy. He does not, without regard for anything, have mercy on the unworthy and punish the worthy.
If we settle on this interpretation, we must add this supposition. Saint Paul introduced this saying in order to dispose those perplexed by the fact that not all Jews entered into possession of the blessings of the promised Deliverer. They should resolve this perplexity not by any outward factors that catch the eye, but from the idea of God as all-righteous and all-good.
It is as though he said: God has mercy on whom He wills. So also among you, He chooses whom He wills. But since there is no unrighteousness with God, there is none in this action of His either. Entrust everything to God and be at peace. Believe that here the promise has not failed.