"If it were not so, I would have told you." (John 14:2)
It made me wonder what else Jesus told us that was a correction of something we've heard but that isn't so.
Jesus said things like
"You have heard it said ..., but I tell you ..."
Do some say that Jesus came to abolish the Law of Moses? Not so, he said. "I tell you the truth, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law until everything is accomplished." Jesus came to accomplish - not to abolish - the Law of Moses (Matthew 5:17-20) And since the disappearance of heaven and earth is part of things yet to be accomplished, the Law remains to this day.
The Law forbids murder, for instance. Jesus tells us also that anger without cause toward a brother is to be resolved, and to reconcile with a brother upset with you. Be careful what you call him. (Matthew 5:21-22)
Or adultery. How do you define the word "commit"? Jesus said yes, the physical act of adultery is forbidden, but tells us the mental or spiritual act of committing it is also forbidden. (Matthew 5:27-28)
It has been said that to divorce a wife requires a certificate of divorce. But Jesus said divorce for any reason other than marital unfaithfulness causes future adultery.
Similarly, there is more to not breaking an oath. Don't swear at all.
There is more to "an eye for an eye". Don't resist evil happening to you.
It's been said "love your neighbor and hate your enemy." Instead, love your enemies and pray for those who persecute you. Get in line with the Father's way. (Matthew 5:33-48)
More things that Jesus emphasized "I tell you...":
Matthew 6:25 - don't worry about your life
Matthew 8:10 - what faith!
Matthew 10:23-42 - prepare for His return
Matthew 11:11 - of John the Baptist
Matthew 12:5-6 - truth of One
Matthew 17:12 - of Elijah
Matthew 17:20 - of faith
Matthew 18:13 - of shepherd's happiness
Matthew 19:23-24 - of rich men
Matthew 19:28 - rewards at time of renewal
Matthew 21:21 - work possible with doubtless faith
Matthew 21:42 - explaining Psalm 118:22-23
Matthew 23:39 - when will Jerusalem see Messiah again?
More on I tell and tell truth searches
Jesus told us the way of perfection, as the Father in heaven is perfect. People who heard his "sermon on the mount" were amazed at Jesus' authority (Matthew 7:28-29). Following the sermon by healing various people was amazing as well. There was something different about hearing Jesus extending the reach of the Law. If he hadn't been living up to this kind of Law living, surely the people would have noticed hypocrisy. Oral tradition had made some changes in the Law, and that is where Pharisees found objection with Jesus' actions, such as healing on the Sabbath.