we seek
That is, "we" Jews. (Romans 3:19-23). The passage might be thus paraphrased: If we Jews, in seeking to be justified by faith in Christ, take our places as mere sinners, like the Gentiles, is it therefore Christ who makes us sinners? By no means. It is by putting ourselves again under law after seeking justification through Christ, that we act as if we were still unjustified sinners, seeking to become righteous through law-works. (Galatians 5:1-4).
sinners
Sin
( See Scofield) - (Romans 3:23).