Hebrews 6:16

Verse 16. For men verily swear by the greater. That is, they appeal to God. They never swear by one who is inferior to themselves. The object of the apostle in this declaration is to show that, as far as this could be done, it had been by God. He could not indeed swear by one greater than himself, but he could make his promise as certain as an oath taken by men was when they solemnly appealed to Him. He could appeal to his own existence and veracity, which was at any time the most solemn form of an oath, and thus put the mind to rest in regard to the hope of heaven. And an oath for confirmation. An oath taken to confirm or establish anything. Is to them an end of all strife.