2. It is for their obstinacy in sin, their being so long accustomed to it that there was little hope left of their being reclaimed from it (v. 23): Can the Ethiopian change his skin, that is by nature black, or the leopard his spots, that are even woven into the skin? Dirt contracted may be washed off, but we cannot alter the natural colour of a hair (Matt. v. 36), much less of the skin; and so impossible is it, morally impossible, to reclaim and reform these people. (1.) They had been long accustomed to do evil. They were taught to do evil; they had been educated and brought up in sin; they had served an apprenticeship to it, and had all their days made a trade of it. It was so much their constant practice that it had become a second nature to them. (2.) Their prophets therefore despaired of ever bring them to do good. This was what they aimed at; they persuaded them to cease to do evil and learn to do well, but could not prevail. They had so long been used to do evil that it was next to impossible for them to repent, and amend, and begin to do good. Note, Custom in sin is a very great hindrance to conversion from sin. The disease that is inveterate is generally thought incurable. Those that have been long accustomed to sin have shaken off the restraint of fear and shame; their consciences are seared; the habits of sin are confirmed; it pleads prescription; and it is just with God to give those up to their own hearts' lusts that have long refused to give themselves up to his grace. Sin is the blackness of the soul, the deformity of it; it is its spot, the discolouring of it; it is natural to us, we were shapen in it, so that we cannot get clear of it by any power of our own. But there is an almighty grace that is able to change the Ethiopian's skin, and that grace shall not be wanting to those who in a sense of their need of it seek it earnestly and improve it faithfully.