13 but exhort one another daily, while it is called “Today,” lest any of you be hardened through the deceitfulness of sin.
One way to help fellow Christians from developing a hard heart is to constantly encourage each other in the truth.
The word “but” is a strong contrast to what has gone before in the preceding verse. Christians who disbelieve what God can do need exhortation.
exhort [entreat] one another daily,
Christians ought to exhort one another day by day; they are to do this each day. They need to constantly watch out for each other. One exercise of exhortation is not enough. Believers have a mutual duty because they have a mutual God and mutual spiritual interests.
“Exhort” comes from two words para (alongside) and kaleo (to call); Christians are to call fellow believers alongside themselves to help them.
while it is called “Today,”
Christians are to deal with their sins while they have opportunity. They are to deal with a present reality. The day may come when some are so hardened by sin that they become insensitive to it and to God. We have no promise for tomorrow. Mature readers of Hebrews must decisively help doctrinally weak believers. They need help vulnerable believers to act upon God’s promises without delay.
God gives each of us a “today” that we are to keep day-by-day.
Satan uses resolutions; his wish is for us to put them off until tomorrow. He does not care about the resolution so long as we don’t fulfill it.
Each Christian is to press on with their lives and live them day-by-day. If we don’t then we might be hardened by sin’s deceitfulness, by willful rejection of God’s Word. It is important for believers today not to repeat the same experience of the Israelites. If we fortify our hearts against the Word, then it cannot possibly speak to our souls.
Christians have a corporate as well as individual responsibilities. God expects us to help fellow believers who go astray.