But exhort one another (literally, yourselves, as in Colossians 3:16, the idea being that of the responsibility of the believers themselves in keeping their own faith alive; the Church must keep itself from apostasy by the mutual admonitions of its members), day by day, so long as it is called Today (i.
e. while the "Today," τὸ σήμερον, of the psalm is still called so, καλεῖται: while you are still living day by day within the limit of its meaning); lest any one of you be hardened (still referring to the warning of the psalm) by the deceitfulness of sin.
Here again, as in Hebrews 3:12, the possible result of obdurate unbelief is distinctly traced to moral culpability. Sin is a deceiver (cf. Romans 7:11; Ephesians 4:22); it distorts the spiritual vision, causes us to take false views of things, and to lose our clear view of truth; and continued dalliance with sin may hare its result in final obduracy, which, as above remarked, is our own doing as it comes of our sin, God's doing as it comes of his judgment.
The sin contemplated in the ease of the Hebrew Christians as not unlikely to have its result in obduracy was, not only imperfect appreciation of the true character of the gospel revelation, and consequent remissness in mutual admonition and attendance at Christian worship (Hebrews 10:25), but also, as a further consequence of such remissness, failure in the moral purity of life, the active charity, the disentanglement from the world, and the endurance of persecution, required of Christians.
This appears from the earnest exhortations that follow afterwards against all such shortcomings (see especially Hebrews 10:19-26, Hebrews 10:32-39; Hebrews 12:1-18; Hebrews 13:1-20). It was especially by conscientious perseverance in the religious life that they might hope to keep their religious faith steadfast and unclouded to the end; in accordance with Christ's own saying, "If any man will do ( θέλη ποιεῖν) his will, he shall know of the doctrine, whether it be of God."