<p>3:13- see on 1 Cor. 10:21.</p><p><i>But encourage one another day by day, so long as it is called today, lest any one of you be hardened by the deceitfulness of sin</i>- See on :7 for the significance of &quot;today&quot;. As noted on :12, the Hebrews were to not only worry about their own salvation but that of others. They were to enourage one another daily, which suggests the audience were daily with each other. This would fit the situation in the Jerusalem church, where it seems they daily encountered each other (Acts 2:46). It was the deceitful nature of sin which could harden their heart; but the 'heart' problem was a disbelief in the sure salvation available in Jesus. But ultimately it was sin which was deceiving them, albeit under the guise of claiming to be more rigorously legally obedient to Judaism. The final issue is between sin and righteousness; the kingdom of this world or the eternal Kingdom of God and His Son; the life of the flesh or the Spirit. It was sin which was attractive to them, and we can infer that this was the fundamental reason they were shying away from confident faith in their salvation. For if we are sure we are to live eternally in God's Kingdom in the spiritual life, we can hardly be enthusiastic for the way of the flesh in this life. So it is the desire to sin which militates against total confidence in salvation.</p>