Keep the heart. 1. Because it falls directly under the inspection of God. Man can judge only by what is external, but "I, the Lord, search the heart." 2. Because of the influence the heart has upon the life. He that is concerned about making the tree good will probably make the fruit so. 3. Care in keeping the heart is greatly to be regarded for itself. Is there nothing pleasant, nothing honourable in being masters at home--in being possessors of our own spirits? Is it nothing that the peace of the kingdom is broken, even though the constitution of it be not overthrown?--_Doddridge._ A heart purified by the grace of God, and firmly rooted in truth as its ground, is the source and common fountain for the successful development of all the main activities and functions of human life, those belonging to the sphere of sense, as well as to the psychical and spiritual realms, and this must more and more manifest itself as such a centre of the personality, sending forth light and life.--_Lange's Commentary._ Though to keep the heart be God's work, it is man's agency. Our efforts are his instrumentality.--_Bridges._ All vital principles are lodged there, and only such as are good and holy will give you pleasure. The exercises of religion will be pleasing when they are natural, and flow easily out of their own fountain.--_John Howe._ Although Solomon repeats himself, he always advances upon the thought. There is always some characteristic novelty: and that novelty is the hinge of the purpose, and imbeds its meaning in the life of the passage. Here it is the function of the heart. It circulates life. Give it good blood, and it will throw off disease; give it bad blood, and it will produce disease. Give it health enough, and it will throw off incipient mortification; give it no health, and it will produce mortification. Solomon weaves this into experimental godliness. . . . Guard the great central guard-post, and no out-station will be cut off. If it be, for a time, the heart will win it again.--_Miller._ Verse 24. While we speak, we should never forget that God is one of the listeners. . . . Take the principle of Hagar's simple and sublime confession, accommodated in thought to the case at hand "Thou, God, _hearest_ me." If our words were all poured through that strainer, how much purer and fewer they would be.--_Arnot._ It is true that vigilance over the heart is vigilance over the tongue, inasmuch as out of the abundance of the heart the mouth speaketh. . . . There is no surer index of the state of the "inner man." As is the conversation, so is the heart.--_Wardlaw._