Matthew 5:33

Jesus next gave a condensation of several commands in the Old Testament that forbade taking an oath, invoking the Lord’s name to guarantee the oath, and then breaking it (Exodus 20:7; Leviticus 19:12; Numbers 30:2; Deuteronomy 5:11; Deuteronomy 6:3; Deuteronomy 23:21-23). God has always intended simple truthfulness in speech as well as lifelong marriage. The rabbis had developed an elaborate stratification of oaths. They taught that swearing by God’s name was binding, but swearing by heaven and earth was not binding. Swearing toward Jerusalem was binding, but swearing by Jerusalem was not. In some cases they even tried to deceive others by appealing to various authorities in their oaths. [Note: Hogg and Watson, p. 54.] Jesus was not talking about "cursing" here but using oaths to affirm that what one said was true.