Jesus condemned swearing in His Sermon on The Mount. (Matthew 6:37-38) Many have questioned the difference between this and cursing. This is not the sin of “cursing.” It is the sin of using oaths to affirm that what is said to be true.
This is just one trick used by the Pharisees to sidestep the truth. They would not use the holy name of God, but would come close by swearing by Jerusalem, heaven, earth or some part of the body.
Jesus taught that our conversation should be so honest, and our character so true, that we would not need “crutches” to get people to believe us. “In the multitude of words, there wanteth not sin; but he that refraineth his lips is wise.” (Proverbs 10:19) The more words a man uses to convince us, the more suspicious we should be.