What does Galatians 2:19 mean?

Paul is making the case that nobody can be justified before God by following the works of the law. One can only be justified before God by faith in Christ (Galatians 1:8–9; 2:16).

In the middle of that argument, this is a complicated verse to fully understand. What Paul seems to be saying is that the penalty for not keeping the law perfectly was death. Paul, as a former Pharisee who loved the law of Moses, understood that he had not kept it perfectly. The law revealed just how sinful Paul was and condemned him to death. In comparison to a perfect, holy God, nothing less than perfection is owed. If we sin, at all, in any way, then we're unworthy to be in His presence. We cannot be "justified" to a perfectly holy God, because we are not holy!

Christ, though, paid the penalty Paul owed for failing to keep the law. This is what allows God to "declare" us justified, though we ourselves have sinned. Jesus died in Paul's place. Once dead, someone is dead to everything, including the law. So Paul, through Christ, died to the law. That freed him to truly "live to God." As he will say in the following verse, he died with Christ and now lives by faith in Christ.