The teachings of our Lord are like the headings of chapters, which are filled out and developed in the writings of the apostles. This is remarkably true of the Sermon on the Mount, which, without going largely into details, sets forth the principles which are to govern His kingdom on earth. The application and interpretation of these principles, He leaves to the inspired apostles and evangelists, who continued to teach and preach after His departure, and to the Holy Spirit who is promised to the believing church as its guide, teacher and comforter until Christ Himself shall come again. But besides many precepts and injunctions which imply holiness, there are several, also, which expressly require it. Among the beatitudes at the beginning of the Sermon, we find this striking statement: "Blessed are the pure in heart for they shall see God." Now, heart purity cannot exist while there is any sin in the heart. Wherever there is sin in the heart, whether actual or indwelling, there is also defilement; and purity and defilement are incompatible terms. Heart purity, therefore, is identical with entire sanctification, and heart purity is not only a great energizer, so that a man is powerful for good in proportion to the purity of his heart and life, but it is also a great illuminator, so that it enables its possessor to see God. This, of course, does not imply an open or an outward vision, but a spiritual apprehension of God, whereby we are brought into fellowship and communion with Him, and in a spiritual sense, we maybe truly regarded as seeing Him who is forever invisible to outward sense. This inward purity, as distinguished from a blameless outward walk, was by no means unknown to the Old Testament writers. In the Twenty-fourth Psalm, David asks the question "Who shall ascend into the hill of the Lord? or who shall stand in His holy place?" And He immediately answers it by saying, "He that hath clean hands and a pure heart." The clean hands imply that his works are in accordance with God's law; in other words, that his outward life is free from condemnation. But the "pure heart" means more than this, and suggests what the same royal Psalmist remarks again in the Fifty-first Psalm. "Behold, thou desirest truth in the inward parts, in the hidden part, Thou shalt make me to know wisdom." It is also noticeable in the Twenty-fourth Psalm, as already quoted, that the clean hands or justification comes before the pure heart or entire sanctification. So accurate is the blessed spiritual logic of the Holy Ghost. Returning to the Sermon on the Mount, we find at the end of Matthew fifth the direct command, "Be ye, therefore, perfect, even as your Father which is in heaven is perfect," or if we take the Revised Version, which is more accurate in translation, the command becomes a positive assertion, which is equally forcible. "Ye, therefore, shall be perfect as your Heavenly Father is perfect."