Romans 2:2-3 — But we are sure that the judgment of God is according to truth against them which commit such things.
And thinkest thou this, O man, that judgest them which do such things, and doest the same, that thou shalt escape the judgment of God?
According to the truth — according to facts with nothing hidden, according to God's unerring assessment.
Judgment — In verse 2 "judgment" is an adverse sentence. In verse 3, it is the carrying out of the sentence.
Paul is referring to the moralizer who is of the opinion that he doesn't sin because he doesn't sin outwardly and that he will escape judgment. Paul says that that person sins inwardly (and probably outwardly too) and will not escape judgment.