Adam Clarke on Hebrews 12:29

For our God is a consuming fire - The apostle quotes Deu 4:24, and by doing so he teaches us this great truth, that sin under the Gospel is as abominable in God's sight as it was under the law; and that the man who does not labor to serve God with the principle and in the way already prescribed, will find that fire to consume him which would otherwise have consumed his sin.