And they took Joseph's coat, and killed a kid of the goats, and dipped the coat in the blood;

Jamieson-Fausset-Brown Bible Commentary

31-33. they took Joseph's coat-The commission of one sin necessarily leads to another to conceal it; and the scheme of deception which the sons of Jacob planned and practised on their aged father was a necessary consequence of the atrocious crime they had perpetrated. What a wonder that their cruel sneer, "thy son's coat," and their forced efforts to comfort him, did not awaken suspicion! But extreme grief, like every other passion, is blind, and Jacob, great as his affliction was, did allow himself to indulge his sorrow more than became one who believed in the government of a supreme and all-wise Disposer.

Matthew Henry's Concise Commentary

37:31-36 When Satan has taught men to commit one sin, he teaches them to try to conceal it with another; to hide theft and murder, with lying and false oaths: but he that covers his sin shall not prosper long. Joseph's brethren kept their own and one another's counsel for some time; but their villany came to light at last, and it is here published to the world. To grieve their father, they sent him Joseph's coat of colours; and he hastily thought, on seeing the bloody coat, that Joseph was rent in pieces. Let those that know the heart of a parent, suppose the agony of poor Jacob. His sons basely pretended to comfort him, but miserable, hypocritical comforters were they all. Had they really desired to comfort him, they might at once have done it, by telling the truth. The heart is strangely hardened by the deceitfulness of sin. Jacob refused to be comforted. Great affection to any creature prepares for so much the greater affliction, when it is taken from us, or made bitter to us: undue love commonly ends in undue grief. It is the wisdom of parents not to bring up children delicately, they know not to what hardships they may be brought before they die. From the whole of this chapter we see with wonder the ways of Providence. The malignant brothers seem to have gotten their ends; the merchants, who care not what they deal in so that they gain, have also obtained theirs; and Potiphar, having got a fine young slave, has obtained his! But God's designs are, by these means, in train for execution. This event shall end in Israel's going down to Egypt; that ends in their deliverance by Moses; that in setting up the true religion in the world; and that in the spread of it among all nations by the gospel. Thus the wrath of man shall praise the Lord, and the remainder thereof will he restrain.