2:21 I do not nullify the grace of God, for if righteousness comes through the Law, then Christ died needlessly (NIV – for nothing).
The Greek word charis—as here usually translated as “grace”—refers to something that gives joy in loving-kindness. The “grace of God” is His merciful kindness, as stated by the previous verse, the Son of God “loved me and gave Himself up for me”.
The word “righteousness” in this verse is a synonym for “justified”. It means to be reconciled to God. The GNB renders the Greek word in 2:21 as “put right with God” (2:21). Righteousness is something that man can receive from God through His loving-kindness:
“if righteousness comes through the Law, then Christ died needlessly” (2:21)
“For if a law had been given which was able to impart life, then righteousness would indeed have been based on law” (3:21)
“Even so Abraham BELIEVED GOD, AND IT WAS RECKONED TO HIM AS RIGHTEOUSNESS” (Gal. 3:6 also Rom. 4.3)
“… those who receive … the gift of righteousness will reign in life through the One, Jesus Christ” (Rom 5:17).
“Gentiles, who did not pursue righteousness, attained righteousness, even the righteousness which is by faith” (Rom. 9:30)
In 2:21 Paul is, by implication, accusing the Galatians that they “nullify the grace of God” by striving for “righteousness … through the Law”. To explain:
To strive to become right before God “through the Law” means to strive to be put right before God by your own effort. That is not possible for man to do. Man is utterly sinful.
If man was able to be right before God by his own effort, then “Christ died needlessly”.
But since man is totally unable, God, in His merciful kindness (grace), gave Christ to die for our sins so that we might be reconciled to God simply on the basis of faith (2:16).
To be justified by faith means to be justified by grace (by His merciful kindness – Rom. 4:16), because one’s faith does not merit justification.
The Galatians, by “seeking to be justified by law” (5:4), “nullify the grace of God” (2:21). To them “Christ will be of no benefit” (5:2). This is why Paul views the distorted gospel in such a serious light that he would even curse the people that teach this distorted “gospel” (1:8-9).