Christ put into simple words some of the great rules for the interpretation of life.  “By their fruits ye shall know them,” has become a part of the language of the civilized world.  “Do men gather grapes of thorns, or figs of thistles?” He asks.  “A good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit.”  Here a great spiritual principle was announced.  We must consider the nature; nothing less than a change in the nature can change the fruit.  A bad heart is just as sure to bring forth bad thoughts and bad deeds as the thistle is to bring forth thorns.  And so the good heart is just as sure to yield good deeds as the grape-vine is to yield grapes or the fig-tree is to yield figs.  Look at the tree, therefore; the fruit will take care of itself.

In the Sermon on the Mount, in which He embodied such a wealth of moral precept and spiritual counsel, He warned against investments in that which would divert the affections from the great purpose of life.  “Lay not up for yourselves treasures on earth, but lay up for yourselves treasures in heaven.”  “For where your treasure is, there will your heart be also.”  It was the heart that He dealt with—­always the heart, in which man does his decisive thinking and out of which are “the issues of life.”

The Master dealt with the beginnings of evil.  He did not wait until the sin had been completed or the wrong accomplished.  He cut out the bad purpose at its birth before it had time to develop.  He says: 

And if thy right eye offend thee, pluck it out, and cast it from thee:  for it is profitable for thee that one of thy members should perish, and not that thy whole body should be cast into hell.  And if thy right hand offend thee, cut it off, and cast it from thee:  for it is profitable for thee that one of thy members should perish, and not that thy whole body should be cast into hell (Matt. 3:  29).

This may seem like a harsh doctrine and yet it is merely an application to morals of a salutary principle that all understand when applied by the surgeon.  A finger is often removed in order to save the hand; a hand is removed to save the arm; and an arm is removed to save the body.  An eye, too, is often removed to save the sight of the remaining eye.  Is eye or arm or body more important than the soul?

Christ understood relative values in the spiritual world.  He used the material things in life to illustrate values in the realm of the ideal; He used the things that are seen to make understandable the eternal things that the senses cannot comprehend.

And what called forth this powerful illustration—­the sacrificing of the right eye and the right hand to save the body?  He was laying the foundation for a great moral reform, namely, the single standard of morality.  He was attacking a great sin and, as usual, He laid the axe at the root of the tree.  He was dealing with adultery and He traced the sin to its source.  He would purge the heart of the unclean thought; He would put a ban on the desire before it found vent in accomplishment.  He turned the thought from the body to the heart and to the soul.