Genèse 32:13

But Thou hast promised, I will surely do thee good, and will make thy sons many as the sand of the sea be numbered for that cannot be numbered for multitude.

AND THOU SAIDST: I WILL SURELY DO THEE GOOD. Even though he was afraid lest the sin cause him to lose that which he was promised, Jacob said: “You have done great kindnesses for me even though I was unworthy of them. Certainly You will do for me this undeserved kindness which You have promised me, namely, that You will bestow good upon me and increase my seed. My sin should not withhold from me the good You have promised me, for in the beginning I was also unworthy of it had You marked against me mine iniquities. And You did not promise it to me on account of my deeds, but only out of Your abundant mercies.”
And some commentators say that Jacob had compassion for his children and household lest Esau smite them, because he did not know whether the promise, And thy seed shall be as the dust of the earth, applied to these or to others, it being possible that he himself would escape and have additional children. But in my opinion this is not correct, for if this was his thought, how did he say in his prayer, And Thou saidst: I will surely do thee good and make thy seed as the sand of the sea? Moreover, it was told to him in Beth-el, And behold, I am with thee, and will keep thee whithersoever thou goest, and I will bring thee back into this land. If his children were to fall before his brother’s sword, this promise would not be fulfilled, and it is to this promise that Jacob alluded when he said, And Thou saidst: I will surely do thee good. Similarly with the promise, And I will do thee good: all this Jacob said on the basis of it having been said to him, And I will be with thee., 31:3. But all his misgivings were on account of the fear of sin, for it is the way of the righteous to be always fearful. Thus Jacob was fearful that perhaps even after he left Haran, he sinned by entering into a covenant with Laban, who was an idol-worshipper, or in some other matter, and Who can discern errors?

ואתה אמרת היטב איטיב עמך; even though You are under no obligation to keep the promise You have made to me seeing that I am not worthy of it, do it for the sake of Your Holy Name which obligates You to keep Your promises (as Moses argued when he reasoned with You not to destroy Israel in spite of their having sinned with the golden calf. His argument had been: “Why should the impression be created that You are unable to keep promises You have made?”) The argument used by Moses he used more than once when he repeated it after the sin of the spies (Numbers 14,16)

ואתה אמרת היטב איטיב עמך, if what I am afraid of were to happen this would be the reverse of Your promise to me. How can I watch the destruction of my family?

ושמתי את זרעך, even if only my children will be killed this will be the opposite of what You promised. It behooves You to let them survive for the sake of Your great name, even if I myself do not deserve to survive. We use this kind of argument in our prayers when we say (based on Jeremiah 14,7) אם עונינו ענו בנו עשה למען שמך, “if our sins testify against us, (save us) for the sake of Your name!”

ואתה אמרת, Yaakov’s formulation is reminiscent of that of David in Psalms 119,49 “remember Your word to Your servant through which You have given me hope.”

היטב אטיב עמך, it is the custom for Scripture to write the verb in the infinitive mode together with the appropriate mode of the verb in order to reinforce what the verb expresses. According to Bereshit Rabbah 76,7 the word היטב refers to G’d’s support for Yaakov based on his merits, whereas the word איטיב refers to G’d’s support for him based on the merit of his father and grandfather.

כחול הים, an inaccuracy, as in the verse Yaakov referred to G’d had promised that his descendents would be as numerous as the “dust of the earth,” not like the sand on the beaches of the sea. (28,14) The change in syntax is irrelevant, as we explained repeatedly that when the Torah repeats the same theme with different words, the reason is not to alert the reader to an additional dimension of the message, but only to stress the message, to draw attention to its importance.