Good question Rachel Rachel (did you already know this ? ) >>
"Seeming Contradictions Between the Mosaic Law and the Sermon on the Mount
There are a few cases where Christ interprets the Law of Moses in such a way as to create seeming difficulties. We read for example in Matt. 5:21-22, “Ye have heard that it was said by them of old time, ‘Thou shalt not kill; and whosever shall kill shall be in danger of the judgment:’ But I say unto you, that whosoever is angry with his brother without a cause shall be in danger of the judgment:….whosoever shall say, ‘Thou fool, shall be in danger of hell fire” (Gr. “gehenna”).
Note the contrast between what was written in the Mosaic Law and what Christ preached. This is not an error; it is a very legitimate contrast. It is an excellent example of Christ setting a higher standard for the believer than the standard set by the Mosaic Law. Because Christ is God He, of course, has every right to do just that.
Consider also Ex. 21:23-25 where we see that the law required “life for a life, eye for an eye”. But we read in Matt.5:38 where Jesus said, “Ye have heard that it hath been said, ‘An eye for an eye, and a tooth for a tooth: But I say unto you, that ye resist not evil: but whosoever shall smite thee on thy right cheek turn to him the other also”. Here too there is a contrast in the words, “But I say”. Again, this is not an error; it is Christ’s right as God to set a higher standard for believers to live under than the standard set by the Mosaic Law.
And let us also consider Numbers 30:2 where we read “If a man vow a vow unto the Lord or swear an oath to bind his soul with a bond; he shall not break his word……”. And in Matt. 5:33-34 we read, “Again, ye have heard that it hath been said by them of old times, ‘Thou shalt not forswear thyself, but shalt perform unto the Lord thine oaths’. But I say unto you, ‘Swear not at all…..but let your communication be, ‘Yea, yea’…….’”.
Christ, as the Author of the Law, had every right to demand a higher standard, and that is what He did as demonstrated in these verses quoted above."