The test our Lord gives for "discerning the spirits" is one which requires time for its application, but it is the only sure one; and when we remember that the Master is now looking forward into the future history of His kingdom, we can see why He should lay stress on a test whose operation, though slow, was sure. It is of course assumed that the first criterion is the Word of the Lord Himself. This is the law of the kingdom; but, knowing well what was in man, the Lord could not but foresee that there would be those who could so twist any words that might be spoken on those great subjects as to lay snares for the unwary; and therefore, besides the obvious appeal "to the law and to the testimony," He supplied a practical test which, though less speedy in its application, was perfectly sure in its results. The announcement of so important a test leads to the development of the general principle on which its validity depends--viz., the vital connection between essential doctrine and life. In the long run the one is always the outcome of the other. In the spiritual as in the natural world every species brings forth fruit "after its kind." "Do men gather grapes of thorns, or figs of thistles? Even so every good tree bringeth forth good fruit; but a corrupt tree bringeth forth evil fruit. A good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit." The law being so absolute, making it certain, on the one hand, that where there is truth in the inward parts there will be good fruit in the outward life, and on the other, that where there is corrupt fruit in the outward life there must be that which is corrupt in the hidden man of the heart, it follows that the criterion is so sure as to be without appeal: "Every tree that bringeth not forth good fruit is hewn down, and cast into the fire" (ver. 19), and therefore may well determine the question as to who are trustworthy teachers in the Church: "Wherefore by their fruits ye shall know them."