Take heed to yourselves

Take care, brothers, lest there be in any of you an evil, unbelieving heart, leading you to fall away from the living God. But exhort one another every day, as long as it is called "today," that none of you may be hardened by the deceitfulness of sin.
Hebrews 3:12-13, ESV

This verse is startling. The warning is given with an illustration from Israel's history. A nation that had been redeemed from slavery, invited into an intimate covenant relationship with God, and given a promised land to occupy failed to receive it because they did not believe God, and continually disobeyed and grumbled against Him (with the exception of two men of their generation who feared and obeyed God). The "falling away" referred to is not just some temporary cold moment in their relationship with God. It is a total cutting off of these once liberated people from God, by their own continual and willful disobedience - a mark of unbelief. The entire record of events in the Old Testament, as well as the record in Hebrews 3:7-19 through Hebrews 4:1-6 makes this clear. The words of warning used throughout these passages are strong.

Therefore, while the promise of entering his rest still stands, let us fear lest any of you should seem to have failed to reach it.
Hebrews 4:1, ESV

Our New Covenant redemption mirrors the salvation of the Israelites from the bondage of Egypt. We have been redeemed from the slavery of sin and satan, are now partaking of a New Covenant sealed with Jesus' Blood, and are promised eternal life with God. The fearful record of this falling away is highlighted for us because it too may describe our own condition - if we do not give heed to ourselves. The danger is nearer than we may think, precisely because of the "deceitfulness of sin." It is so near that we are told to exhort one another, every single day. This means that our daily conversation with fellow disciples of Christ ought to contain sincere communication to keep one another accountable, provide encouragement and if necessary, admonition. It seems like such a small thing to do when you consider what's at stake, but there really is power in keeping these fearful realities, and the truth of Scripture, in the forefront of our mind on a daily basis.

Jesus Christ Himself exhorts us:

“But take heed to yourselves, lest your hearts be weighed down with carousing, drunkenness, and cares of this life, and that Day come on you unexpectedly."

Luke 21:34

"But the one who endures to the end will be saved."

Matthew 24:13, ESV