“Jacob tore his clothes.” Tearing the clothes was an ancient and widely practiced custom. A person would tear his clothes as a sign of grief, mourning, or anguish. It occurs here in Genesis, and it was still being practiced during the early Church (Acts 14:14). When it came to the High Priest in Israel, his clothing was considered sacred, so he was not allowed to tear his clothes (Lev. 21:10). At the trial of Jesus Christ, the High Priest became so enraged at Jesus saying he was the Messiah that he ignored God’s command and tore his clothes (Matt. 26:65).
Although there was no set way to tear one’s clothing, in the last couple centuries missionaries to the Middle East reported seeing people grab the top of their garment and tear it (or cut it with a knife) a handbreadth. So apparently tearing the clothes was more of a symbolic act and did not involve tearing the garment from top to bottom. Tearing one’s clothing is mentioned many times in the Bible (Gen. 37:29, 34; 44:13; Num. 14:6; Josh. 7:6; Judg. 11:35; 1 Sam. 4:12; 2 Sam. 1:2, 11; 13:19, 31; 15:32; 1 Kings 21:27; 2 Kings 5:7; 6:30; 11:14; 18:37; 19:1; 22:11; Ezek. 9:3; Esther 4:1; Job 1:20; 2:12; Isa. 36:22; 37:1; Jer. 41:5; Matt. 26:65; Acts 14:14).
“and mourned for his son many days.” The Bible does not say how long, but from the fact that his children tried to comfort him but he rejected it tells us that it was longer than customary.