Answer
Using the phrase I swear to God may be right or wrong depending on the context. In a court of law, those called to the witness stand traditionally place a hand on a Bible and swear before God to tell the truth. In such an instance, the holiness and power of God are called as a witness to the proceedings. The invocation of God’s Word is meant to make the one testifying soberly aware of God’s presence, as God’s honor and righteousness are held up as a standard. However, in other cases, “I swear to God” is used as a tagline or in jest, and the character of God is never even considered. This is wrong. It is similar to the flippant “Oh, my God!” that is so common today.
One of the first commandments God gave to mankind is this: “You shall not take the name of the Lord your God in vain” (Exodus 20:7). There are many ways we take God’s name in vain. One way is to use God’s name as a swear word or for emphasis (“God, no, I won’t do that!”). Such expressions are disrespectful and indicate that the speaker has little awareness of the One whose name he uses so carelessly.
Likewise, we should not invoke God’s name at the end of outrageous statements, as though tossing God’s name into the mix makes our words trustworthy. Saying things like “It was the biggest fish in the lake! I swear to God!” is a flippant use of God’s name. We should avoid saying “I swear to God” in such contexts, as well as similar expressions such as “God’s honest truth” or “God as my witness.”
Jesus directly taught on this subject: “You have heard that it was said to the people long ago, ‘Do not break your oath, but keep the oaths you have made to the Lord.’ But I tell you, Do not swear at all: either by heaven, for it is God’s throne; or by the earth, for it is his footstool; or by Jerusalem, for it is the city of the Great King. And do not swear by your head, for you cannot make even one hair white or black. Simply let your ‘Yes’ be ‘Yes,’ and your ‘No ,’ ‘No’; anything beyond this comes from the evil one” (Matthew 5:33–37). Basically, Jesus says that, if you say something, people should be able to assume that it’s true, without the addition of various oaths. All you need to say is “yes” or “no.” Your word should be good. There’s no need to swear on this or that, and there’s certainly no reason to “swear to God” in our conversations.
There is nothing in Scripture that prohibits us from taking formal oaths, making solemn promises, or signing contracts. Using the words I swear to God in such solemnities is proper and acceptable. We are never discouraged from making careful, thought-out promises such as wedding vows.
“Let them praise your great and awesome name—he is holy” (Psalm 99:3). God’s name is to be praised, not used as an exclamation or an afterthought. If we swear to God, it should only be in the context of making a formal vow, as we treat His name with all the reverence and honor He deserves (Hebrews 12:28–29).
