And seeing the multitudes, He went up on a mountain, and when He was seated His disciples came to Him. Then He opened His mouth and taught them, saying… Matthew 5:1-2
The first question we should consider is: to whom did Jesus direct the Sermon on the Mount (SOTM)?
First, an incorrect opinion. Some who unnaturally divide Israel and the Church, and the Old and New Testaments, teach that the SOTM was aimed exclusively at Israel, not Christians, because Jesus spoke these words before He died and rose again. This is yet another grave error made by those who persist in wrongly dividing the truth!
The SOTM is, in one sense, for all people of all time. The teachings of Jesus, though referencing things more known by Jews than by Gentiles of that day, are timeless and not limited to any particular people group other than human beings.
Some point out that while the multitude was present, Jesus addressed His disciples specifically. The text supports this idea, but while disciples are the ones who will most readily understand the SOTM, we dare not say it does not apply to nonbelievers!
The impact of the Sermon on nonbelievers would be conviction of sin as Jesus raises the bar from the mere letter of the Law to the spirit of the Law. The Sermon tells nonbelievers that they are guilty before God and His Law, and therefore need a Savior.
As for non-believers who think that obeying the SOTM is the way to earn entrance into Heaven, they have missed the entire point of the Sermon! They missed on this crucial point in particular:
Matthew 7:22-23 Many will say to Me in that day, 'Lord, Lord, have we not prophesied in Your name, cast out demons in Your name, and done many wonders in Your name?' 23 And then I will declare to them, 'I never knew you; depart from Me, you who practice lawlessness!'
These words clearly communicate the fact that salvation is in knowing and being known by Jesus—not by doing anything, including following the SOTM—which no one but Jesus could successfully accomplish!
The impact of the Sermon in believers is that it instructs us what holy living looks like. It is not merely about actions, but about changed hearts.