Excerpt from What Is the Greatest of All Protestant “Heresies”? by Sinclair Ferguson:

“This is why, as the author of Hebrews pauses for breath at the climax of his exposition of Christ’s work (Hebrews 10:18), he continues his argument with a Paul-like “therefore” (Hebrews 10:19). He then urges us to “draw near … in full assurance of faith” (Hebrews 10:22). We do not need to re-read the whole letter to see the logical power of his “therefore.” Christ is our High Priest; our hearts have been sprinkled clean from an evil conscience just as our bodies have been washed with pure water (v.22).

Christ has once-for-all become the sacrifice for our sins, and has been raised and vindicated in the power of an indestructible life as our representative priest. By faith in Him, we are as righteous before the throne of God as He is righteous. For we are justified in His righteousness, His justification alone is ours! And we can no more lose this justification than He can fall from heaven. Thus our justification does not need to be completed any more than does Christ’s!

With this in view, the author says, “by one offering He has perfected for all time those who come to God by him” (Hebrews 10:14). The reason we can stand before God in full assurance is because we now experience our “hearts sprinkled clean from an evil conscience and … bodies washed with pure water” (Hebrews 10:22).

“Ah,” retorted Cardinal Bellarmine’s Rome, “teach this and those who believe it will live in license and antinomianism.” But listen instead to the logic of Hebrews. Enjoying this assurance leads to four things: First, an unwavering faithfulness to our confession of faith in Jesus Christ alone as our hope (v.23); second, a careful consideration of how we can encourage each other to “love and good works” (v.24); third, an ongoing communion with other Christians in worship and every aspect of our fellowship (v.25a); fourth, a life in which we exhort one another to keep looking to Christ and to be faithful to him, as the time of his return draws ever nearer (25b).

It is the good tree that produces good fruit, not the other way round. We are not saved by works; we are saved for works. In fact we are God’s workmanship at work (Ephesians 2:9–10)!”

Full article is from https://www.ligonier.org/blog/what-greatest-all-protestant-heresies/