It has been some time since I have presented a translation of my own of a Syriac source here. To be honest, I had allowed my command of Syriac to become rusty through neglect, something I have begun trying to rectify. As part of this effort, I present here a translation of a Syriac scholia, or short selective commentary, on a passage from the book of Genesis. The author is Mar Jacob of Edessa, a prominent and productive Syriac Christian bishop and writer of the seventh century (A.D.). This text, while explicating a passage about Cain, the Bible’s first murderer, is really an examination of freedom of will and the mechanics of human wrong-doing, with the verse in question acting as a jumping-off place, and supporting evidence, for the centrality of human freedom in moral action.
Behold! If you do good, I will accept you (Gen. 4:7a): And also, I am accepting of you if you do good. These are an evident indication that God wills the repentance of man, and receives his repentance. And He is longsuffering with him, and gives him also means that call him to this, because He wills his salvation.
But, if you do not do good—upon the door sin is crouching. You are turned towards it and it has mastery over you (Gen. 4:7b): These [words] point out that mastery of the house and freedom of will belong to humans, and that one wills by his own will. One calls to sin that it come upon him and have mastery over his soul. If he does not will it, sin is not able to draw near to him. That is, it crouches upon the door of your mind, like a fierce animal outside of the gate of a house. If you turn towards this by your own will, and open up to it, it enters and has mastery upon you. And if you do not will, it is not able to enter against you.
By means of these you are clearly taught that Satan is not the sower of sin able to compel, or govern with force the rule of the house of the human mind, and sin is not the seed itself of evil. For this Cain was condemned, for he did not come to repentance of these things, though he opened the door to sin by his own will, and it entered and took mastery over him, as God said to him, and he murdered his transgression-less brother, from envy alone.
 That is, mastery of the human body, or perhaps the soul: the exact meaning of the phrase, here literally translated, is a bit ambiguous.