Sforno on Genesis 4:7/ספורנו על בראשית ד׳:ז׳

1הלא אם תיטיב, if only you improve yourself you will also be welcome in My eyes.

2שאת, every lofty level of greatness is lying in wait for you, ready to become yours,

3ואם לא תיטיב לפתח חטאת רובץ, however, sin is also lying in wait for you if you will add further intentional sin to the already performed unintentional sin. This is the way of the evil urge, that once you give into it, it will forever be ready to tempt you again.

4כי אליך תשוקתו, “for it longs for you due to its very nature. It too is anxious to satisfy its desires, its aspirations every day.”

5ואתה תמשול בו, it is within your power to overcome the power of the evil urge thanks to the צלם אלוקים, the divine image with which you have been provided at birth. This conforms to our sages in Sukkah 52 who have taught that were it not for this צלם אלוקים, which represents G’d’s assistance against the evil urge, there would be no way man could cope with temptation. This is what David meant in Psalms 37,33 ה' לא יעזבנו בידו ולא ירשיענו בהשפטו, “the Lord will not abandon him to his power; He will not let him be condemned in judgment.”