THE UNION OF FAITH, THE WORD, AND THE HEART. MARTIN LUTHER:
That uniting or combination of the Word and the hearts is reciprocal. For these three—faith, the Word, and the heart—become one. Faith is the glue or the bond. The Word is on one side; the heart is on the other side. But through faith they become one spirit, just as man and wife become “one flesh” (Gen 2:24). Therefore it is true that the heart is combined with the Word through faith and that the Word is combined with the heart through the same faith. LECTURES ON HEBREWS 4:2
Ronald K. Rittgers, editor Reformation Commentary on Scripture: New Testament XIII: Hebrews, James 57