a solemn appeal to God, permitted on fitting occasions ( Deuteronomy 6:13 ; Jeremiah 4:2 ), in various forms ( Genesis 16:5 ; 2 Sam 12:5 ; Ruth 1:17 ; Hosea 4:15 ; Romans 1:9 ), and taken in different ways ( Genesis 14:22 ; 24:2 ; 2 Chr 6:22 ). God is represented as taking an oath ( Hebrews 6:16-18 ), so also Christ ( Matthew 26:64 ), and Paul ( Romans 9:1 ; Galatians 1:20 ; Phil 1:8 ). The precept, "Swear not at all," refers probably to ordinary conversation between man and man ( Matthew 5:34 Matthew 5:37 ). But if the words are taken as referring to oaths, then their intention may have been to show "that the proper state of Christians is to require no oaths; that when evil is expelled from among them every yea and nay will be as decisive as an oath, every promise as binding as a vow."

These dictionary topics are from
M.G. Easton M.A., D.D., Illustrated Bible Dictionary, Third Edition,
published by Thomas Nelson, 1897. Public Domain, copy freely.