‘I say to you: Do not take an oath at all.’
2 Corinthians 5:14-21; Ps 103(102):1-2. 3-4. 9-10. 11-12; Matthew 5:33-37
It is not really necessary to work out of Jesus was asking us NOT to swear using oaths on Heaven, Earth or Jerusalem because they are too holy to be used this way, or if he is instructing us to not make Oaths at all - the text is a bit vague! What is important is what he then says - that in effect there should be no need in a christian community to make promises on oath: we should simply trust each other to say 'Yes' or 'No'.
Is it not odd that we seem to accept the need in a law court to put a hand a hand on the bible when we promise to 'tell the truth, the whole truth and nothing but the truth' when Jesus asked us to simply make that statement on our own account? I have never understood why. Especially given that approximately 50% of people doing so then go on to lie anyhow!