+IV. The way to keep the heart.+--The vigilance of a sentinel is manifested by his notice of the distant motion of the grass under cover of which the enemy is creeping towards the citadel. He is ever on the look-out for the distant enemy. The watchful general notes the first symptom of mutiny in the army, and treads out the spark before it becomes a flame. So the watchful heart-keeper takes notice of the first movement of rebels within. The thoughts take their rise in the soul under the eye of none but God and the keeper, and he must be on the alert at the first motion. And as when the sentinel sees the first movement of the enemy he never thinks of advancing to fight him alone, but communicates with one who has the power to overthrow him, so when a man becomes aware of the first motion of evil in his heart, God must receive the information--He must be called upon to exercise His power to disperse or take prisoners the thoughts before they can become actions. Keeping of the heart includes a guarding of every inlet of temptation, a watchfulness over the senses, and any organ of the outward man which might lead us into temptation. Hence Solomon exhorts his son to guard his _eyes_ and his _feet._ It has been asserted by some that there is nothing in the mind which has not first been in the senses; and though this is a disputed point, we are quite sure that there is much in the heart, both of good and evil, which entered by those gates. There are thoughts there which have been kindled by what we have seen, as Achan's covetous desires were created by the sight of the goodly spoils of Jericho. The eye of David was the entrance-gate of the thought which ended in adultery and murder. And the feet may lead us in forbidden paths--into the way of temptation--into the society of those whose words, finding entrance by the ear, may sow seeds of impurity within. _OUTLINES AND SUGGESTIVE COMMENTS._ Verse 20. Still he calls for attention. It fares with many of us as with little children, who, though saying their lessons, must needs look off to see the feather that flies by them.--_Trapp._ The former verse having spoken of hearing God's Word, this speaketh of reading it. For the beginning of obedience is to be willing to know what is commanded, and it is a part of performance to have learned what is to be performed. . . . Let God's Word be in our heart, it will be in the midst of it. For the heart hath no outside, all is the midst there: the heart hath no outward show, all there is inward truth.--_Jermin._