What does Matthew 5:34 mean?

The previous verse contained Jesus' now-familiar phrase "you have heard that it was said…" which is His way of introducing the common teachings of religious leaders. Jesus does not always contradict those teachings, but He does explain a more godly, challenging application. God expects His commandments to be taken much more seriously than as tool for legalism and hypocrisy.

Currently, Jesus is speaking about swearing oaths as a way of obligating oneself to a task. Someone who said, "I swear to the Lord to pay you the money" would have to answer to God for their sin if they did not follow through. However, in practice, Israel's religious leaders allowed for a system of debatable oaths to take hold. Swearing by things and places other than the Lord may have been an attempt to imply less serious consequences for the oath-breaker (Numbers 30:2). They may have also tolerated those who claimed that God, not the oath-maker, was to blame if the promise was not kept.

Aspects of this continue into modern culture. Jesus is not speaking of formal, official promises such as contracts, marriage vows, or a courtroom oath. This does, however, apply to moments where a person tries to emphasize their honesty using an oath. In English, a person might say, "I cross my heart," or "may God strike me dead if I'm lying," or simply, "I swear I'll pay you back." The implication is that the oath "guarantees" the person is telling the truth and has good intentions.

Jesus now says flatly that His disciples should not take an oath, at all. They should not swear by anything. The main reason is that a person known for integrity doesn't need to enhance their promises. The upright truth behind a Christian's "yes" and "no" should be strong enough to stand on its own. Another concern is that swearing by something that belongs to God comes too close to swearing by God Himself. Therefore Jesus says not to swear by heaven, because it is God's throne. He will expand on that in the following verses.