Hebrews 3:7-11 (ESV)
Therefore, as the Holy Spirit says,
“Today, if you hear his voice,
 do not harden your hearts as in the rebellion,
on the day of testing in the wilderness,
 where your fathers put me to the test
and saw my works
 for forty years.
Therefore I was provoked with that generation,
and said, ‘They always go astray in their heart;
they have not known my ways.’
 As I swore in my wrath,
‘They shall not enter my rest.’ “
The reason the people of Israel who left Egypt did not enter into the rest of the Promised Land was their rebellion against God (verse 8). But that land was not the ultimate rest to which they were being led by God. It was a picture of the ultimate rest found in Christ. He is the final rest.
We are saved by grace without works. He has done all the work and we get all the benefits. What the writer to the Hebrews is doing here is drawing a comparison between those Israelites and the church. Their experiences serve as a warning to those who profess faith in Christ (I Corinthians 10:6). It is a warning. If we harden our hearts like they did, then we too will not enter the final rest that Christ accomplished for all His people on the cross.
The reason those Israelites found no rest was their hearts. As verse 10 tells us “they went astray in their heart;” The evil of rebellion and idolatry and law breaking that characterized them was rooted in their hearts. Their lives were impure because their hearts were evil. Only grace always, always, always produces holiness. People can make themselves good for awhile and in many ways people can live lives that are good in many ways. But those lives will never be the holiness that God requires for eternal fellowship with Him. The Israelites who left Egypt perished because of their unbelief (Verse 19).
So, was it unrighteous living as verse 8 says, or was it unbelief as verse 19 says that caused them to perish? The answer is “yes”. Their unbelief was the cause of their unrighteousness. If they had truly believed they would have turned from sin.
The grace of God is a powerful thing. It is not something that we give lip service to. It is not something that we use to exalt God with our mouths – “I am nothing and am saved by grace alone…” while living a life of sin. It is certainly not something that we can possess and not be changed. Grace is a powerful work of God that turns hearts of stone into hearts of flesh, that opens eyes to the glories of Christ and His work. It regenerates, gives life, grants repentance and faith. It teaches us to say no to ungodliness (Titus 2:11-14). It does it all.
To claim grace and not demonstrate it in holiness of life, holiness of intention, holiness of heart … is to deceive oneself that one truly has encountered the powerful grace of God that the Scriptures talk about. Does this mean that God’s grace at work in a heart will produce sinlessness? The Bible says “no”. But there will be a change. There will be repentance for sin.
Today, bow down before a loving, gracious God who has done it all. Show the world that His grace has done a powerful work in your life. Live, by grace, for the praise of His glory. Pray for His help today to live a God pleasing day. He can do more than you ask or think and He can do it in you (Ephesians 3:20-21.