by Preston Foster

Grace is the gospel.  For some, that seems to be a problem.  Some accuse those who promote salvation by grace through faith alone, as promoting “cheap grace.”
Cheap grace is, at best, an ironic term, as grace is, literally, the most expensive gift ever offered (it cost the life of the only Son of God). Cheap grace is, in fact, a derogatory phrase used to warn grace enthusiasts — and more important, those who are unsure of the critical path to salvation — against too close an embrace of grace.  More to the point, the term is employed to undercut grace itself, intended to make the notion of grace at once dangerous and inadequate.
Cheap grace refers to using grace as license to sin.  As we are sinners saved by grace through faith — and not by any works of the law (Ephesians 2:8-9), “cheap grace” implies that, indeed, there are works that contribute to one’s earning salvation — which is not grace at all.  Indeed, good works are a product of grace (Ephesians 2:10), not a condition for receiving it.  Grace begets good behavior (Galatians 5:16), not vice versa.    
The idea of cheap grace is also a diversion.  I have yet to meet anyone who espouses grace as their license to continue in purposeful sin or premeditated lawlessness (iniquity).  Sin enthusiasts don’t pause to find license to sin.  Neither have I met anyone who has completely stopped sinning.  We all NEED grace.  
The most insidious inference of cheap grace is that one would accept Christ as a vehicle to continue in purposeful sin.  Mere claiming Christ or accepting Him is not the same thing.  If Christ is in you, you are, by definition, different and better (Colossians 2:13; 2 Corinthians 5:17-19).  Dependence on works assumes that the power to live free of sin is man-made, rather than a result of Christ living in you. 
The accusation of cheap grace is, really, a back-door justification for living by the law. The law is positioned as the primary guide for living (1 Timothy 1:7-10), ignoring the Spirit, and discounting the fact that Christ came to live on the earth as a man for the express purpose of keeping the law perfectly — satisfying the requirements of the law, then was crucified as the Lamb of God, taking away the sins of the world — for all time (Hebrews 10:10-12).
The accusation that grace is a cover for sinful desires serves as a pivot point that allows the supposed keepers of the law to pose as guardians of the faith while minimizing the grace provided by Christ on the cross.  It allows them to find comfort their works (or judge the works of others) and their uprightness — believing that their salvation is at least partially earned.  As keepers of the Old Covenant, they reject the fact that New Covenant replaced the Old (2 Corinthians 3:13-15). They see the New Covenant directive of being led by the Spirit (Galatians 5:18) as vague, inadequate, and soft on sin (Romans 6:14). Grace is put on trial.
Those of us who embrace the grace of the New Covenant (Hebrews 10:16-19) and those who hold to the law agree on at least one thing: one of the Covenants is better than the other (Hebrews 8:6-7; Galatians 5:3-4). 
The difference is eternal.