Kommentar zu Bereschit 4:7

הלא אם תטיב IF THOU MENDEST — Its meaning is as the Targum gives it: “if thou wilt improve thy doings, thou shalt be forgiven”.

IS IT NOT THUS, IF THOU MENDEST ‘SE’EITH’. In the opinion of the commentators,⁴²⁵Reference is here to R’dak. So also in Onkelos. this means there is a “lifting” or forgiveness of your sin. And in the opinion of Rabbi Abraham ibn Ezra it means a “lifting” of your face in contrast to [the question G-d asked of Cain]: Why is thy face fallen?⁴²⁶Verse 6. For he who is ashamed presses his face downward. Similarly, it is said, And the light of my countenance they cast not down,⁴²⁷Job 29:24. whereas one who honors him is as if he raises his face upward. This is the sense of the verses: Perhaps he will lift my face;⁴²⁸Genesis 32:21. Meaning, perhaps he will accept me. Do not lift the face of the poor.⁴²⁹Leviticus 19:15. Meaning, do not respect the person of the poor in judgment, but judge in righteousness.
In my opinion the verse means: “If you will mend your ways you will have your rightful superiority in se’eith (dignity) over your brother since you are the firstborn.” And this is the meaning of [G-d’s question to him]: Why art thou wroth?⁴²⁶Verse 6. For by virtue of his feeling ashamed before his brother, his face fell, and because of his jealousy of him he killed him, and now the Eternal told him: Why art thou wroth regarding your brother, and why is thy face fallen on account of him? Is it not thus! If thou mendest, you will have superiority in dignity over your brother, and if thou dost not mend, evil will come upon you not only because of him [your brother], for at the door of your house your sin lurks causing you to stumble in all your endeavors.

הלא אם תיטיב, if only you improve yourself you will also be welcome in My eyes.