If you found out that you had a terminal disease today, and there was a cure for it that you could take, and it was a definite cure, would you take it?
Of course you would. If you had access to it, you would take it, knowing that your terminal disease would be gone. Only a foolish person would not take the medicine.
Then why is it, that when the part of the Gospel that has to do with sin, is presented, many respond with statements like, 'who are you to judge?' or 'let him who is without sin case the first stone.'?
Whenever a standard is presented (a standard of right and wrong), you will hear these phrases. But why? I can come up with two reasons why.
One is, because the person who is making this kind of statement, has seen arrogant 'Christians' holding signs up. pronouncing God's judgment on some group of people. Most of these so called Christians are Pelagians, followers of a doctrine that says an individual is completely responsible for their sins. The Bible says we are responsible to repent and turn away from sin, but sin is part of our fabric since the fall of man, and we are so enmeshed with sin, that it takes a powerful Rescuer to help a person be free from sin. Pelagians don't believe that, and neither do they hold an internal view of sin (sin coming from the heart vs. sin being an action, example, lying or committing adultery, which most of us can choose to not break those laws if we really decide not to do them). It is like chopping off the branches of a tree. You can cut all the branches off, but the root of sin is still there. In time, sin will blossom again unless there is a new root given to the tree (new heart).
The other reason is, people want to hold onto their sin. What happens when a person first hears that lusting sexually after a person whom he or she is not married to, is the same as committing adultery? The person reacts, many times, by saying, 'Judge not, lest ye be judged' (I get a kick out of the KJV language that is often used when people react). Or, they might say, 'He who is without sin, cast the first stone', as if presenting the Law is casting the first stone!
Telling people what God says is right or wrong is not casting the first stone! No one is claiming (except Pelagians) that they are without sin! The same rules apply to me as they do everyone else. It's not like I can commit adultery, but other people can't.
Matthew 7 tells us not to judge, at least in the beginning of the paragraph. The whole point of the paragraph is to deal with our own hearts about our own sins, before we do anything else, then we can help other people deal with their sins. We can't give away what we don't have. We can't teach others how to deal with their sins, unless we have dealt with our own sins first.
The medicine of the Gospel is the cure for our sin sick souls. The Gospel is the only cure for sin. A person would be foolish to not take the medicine of the Gospel, or to believe that the person presenting God's standard hasn't taken the medicine of the Gospel first.