For the word of God is quick, and powerful, and sharper than any two-edged sword, piercing even to the dividing asunder of soul and spirit, and of the joints and marrow, and is a discerner of the thoughts and intents of the heart.
Whenever the Lord addresses us by his word, he deals seriously with us, in order that he may touch all our inmost thoughts and feelings; and so there is no part of our soul which ought not to be roused.
The sum of the whole then is this, — that as soon as God opens his sacred mouth, all our faculties ought to be open to receive his word; for he would not have his word scattered in vain, so as to disappear or to fall neglected on the ground, but he would have it effectually to constrain the consciences of men, so as to bring them under his authority; and that he has put power in his word for this purpose, that it may scrutinize all the parts of the soul, search the thoughts, discern the affections, and in a word show itself to be the judge.
John Calvin’s Commentary on Hebrews 4:12