Therefore if thou bring thy gift to the altar, and there rememberest that thy brother hath ought against thee;
Note 14 at Mt 5:23: The word "therefore" makes Jesus' instructions in this verse and Mt 5:24 a direct result of what He said in Mt 5:21-22. He was saying, "Because the consequences of having strife in your heart are so severe, don't offer a sacrifice to God if your brother is upset with you. Make reconciliation first, and then come and offer your gift."
Notice also that Jesus said, "if your brother has ought against you." It should be clear that we are not supposed to have strife in our hearts toward our brother (Mt 6:14-15; Mr 11:25-26; Jas 3:14-16; 1Jo 2:9-10, and 4:20). But Jesus revealed our responsibility to our brother even when he has hard feelings toward us. We are supposed to take the initiative in reconciliation (Eph 4:32), even as God did with us (Job 42:10 and Ro 5:8).