“Keep thy heart with all diligence; for out of it are the issues of life.” Diligent heart-keeping is essential to a healthy growth in grace. The heart in its natural state is a habitation for unholy thoughts and sinful passions. When brought into subjection to Christ, it must be cleansed by the Spirit from all defilement. This can not be done without the consent of the individual.
When the soul has been cleansed, it is the duty of the Christian to keep it undefiled. Many seem to think that the religion of Christ does not call for the abandonment of daily sins, the breaking loose from habits which have held the soul in bondage. They renounce some things condemned by the conscience, but they fail to represent Christ in the daily life. They do not bring Christlikeness into the home. They do not show a thoughtful care in their choice of words. Too often, fretful, impatient words are spoken, words which stir the worst passions of the human heart. Such ones need the abiding presence of Christ in the soul. Only in His strength can they keep guard over the words and actions.
In the work of heart-keeping we must be instant in prayer, unwearied in petitioning the throne of grace for assistance. Those who take the name of Christian should come to God in earnestness and humility, pleading for help. The Saviour has told us to pray without ceasing. The Christian can not always be in the position of prayer, but his thoughts and desires can always be upward. Our self-confidence would vanish, did we talk less and pray more.
– S.D.A. Bible Commentary, pg. 1157