Jesus testified at His trial with an oath (Matthew 26:64).
Paul made an oath (2 Corinthians 1:23; Romans 1:9). He wrote these words by inspiration from God. Scripture warns against false swearers (1 Timothy 1:10). If all oaths were wrong then this verse would not be in the Bible.
I believe you are referring to James 5:12 and Matthew 5:33-37. They tell us not to swear by heaven or earth or any other oath. This does not mean sincere legal oaths. These verses are talking about the frivolous and profane use of Gods name.
