Is This Practice Off Limits for the Christian?
Swearing oaths is a practice some Christians consider improper. They point out that Jesus says we are not to do this. But the subject needs some consideration, both as to its biblical context, and as to its modern usage. There is ample biblical evidence that this is an acceptable practice for believers under certain circumstances.
Jesus does tell His hearers, "Do not swear at all" (Matt. 5:34; cf. Jas. 5:12), but this command needs to be viewed in its historical surroundings. The Jews of Jesus' day made oaths a part of casual conversation. They became quite adept at manipulating this practice to make it seem like they were telling the truth, when they were not. It is particularly this hypocritical practice that the Lord is speaking against (vs. 33-37).
It should be unnecessary for believers to "swear" to one another that they are speaking the truth, since we are always to do that (Eph. 4:25). However, I do not believe the above injunction prevents a Christian from swearing to his testimony in a court of law, or on other formal occasions. To say, “So help me, God,” is to say “With the Lord’s help I will give you an honest and accurate response. That is merely a recognition that, as weak and fallible creatures, we are in need of divine aid.
We should not take the name of the Lord “in vain” (Exod. 20:7), meaning that we are not to use it carelessly, invoking the Lord’s name to disguise a lie, or to decorate an empty promise we have no intention of fulfilling. That is sinful, and God will hold us accountable for our actions (Deut. 23:21; Ecc. 5:4). However, a vow made sincerely, before God, recognizing His right to hold us accountable, is another matter. In effect, this is what happens when a couple pronounces their wedding vows, or when parents dedicate an infant to the Lord before witnesses.
This kind of swearing is something God Himself did (Heb. 6:13-18). It was actually commanded under certain circumstances in the Mosaic Covenant (Exod. 22:10-11). Ezra called for the swearing of an oath (Ezra 10:5). Jesus gave testimony under oath (Matt. 26:63ff). And Paul does something similar in his epistles (cf. Rom. 1:9; 9:1; II Cor. 1:23; Gal. 1:20). In summary, though the practice is not to be engaged in carelessly or hypocritically, it would seem to be appropriate under certain special circumstances.