Let me hang a bridge between yesterday’s text and our concern today with the unbelief of anxiety. In Hebrews 3:12 it says, “Take care, brethren, lest their be in any of you an evil heart of unbelief, leading you to fall away from the living God.” And verse 14 says, “For we have shared in Christ, if we hold our first confidence firm to the end.”
In other words the evidence that you have come to share in Christ—that you are united to him in saving faith—is that you hold that confidence firm to the end. Perseverance in faith is necessary for salvation. When a person is truly converted, the heart is changed so that now life is lived by faith (Galatians 2:20).
The new birth introduces a person into a life of warfare. That warfare is called the “fight of faith” in 2 Timothy 4:7; 1 Timothy 6:12. And here in Hebrews 3:12 it is called the battle against unbelief. “Take care [that’s the vigilance of battle], brethren, lest there be in you and evil heart of unbelief [there’s the enemy in the warfare], leading you to fall away from the living God [there’s the warning against not taking the warfare seriously].”
In other words the most basic battle of our life is the battle to believe in the living God, and not to allow our heart to become an evil heart of unbelief. Because if unbelief in the living God gets the upper hand in our life, then the result can be a hardening that makes us unwilling to repent and thus cuts us off from the grace of God.
Now this will not happen to those who are truly in Christ. Those who are truly born of God take the battle seriously, and draw on the power of God to fight it, and win it with persevering faith. That is what God promises. “He who calls you is faithful and he will do it” (1 Thessalonians 5:23).
The bridge, then, that I want to hang between last week’s text and this week’s text is the truth that beneath our battle against evil in our heart is the battle against unbelief. Unbelief is the root of evil and the essence of evil. All our sinning grows out of unbelief in the living God and what he has said to us in Scripture.