2:1 Therefore you have no excuse, O man, every one of you who judges. For in passing judgment on another you condemn yourself, because you, the judge, practice the very same things. 2 We know that the judgment of God rightly falls on those who practice such things. 3 Do you suppose, O man—you who judge those who practice such things and yet do them yourself—that you will escape the judgment of God? 4 Or do you presume on the riches of his kindness and forbearance and patience, not knowing that God's kindness is meant to lead you to repentance? 5 But because of your hard and impenitent heart you are storing up wrath for yourself on the day of wrath when God's righteous judgment will be revealed.
6 He will render to each one according to his works: 7 to those who by patience in well-doing seek for glory and honor and immortality, he will give eternal life; 8 but for those who are self-seeking and do not obey the truth, but obey unrighteousness, there will be wrath and fury. 9 There will be tribulation and distress for every human being who does evil, the Jew first and also the Greek, 10 but glory and honor and peace for everyone who does good, the Jew first and also the Greek. 11 For God shows no partiality.
12 For all who have sinned without the law will also perish without the law, and all who have sinned under the law will be judged by the law. 13 For it is not the hearers of the law who are righteous before God, but the doers of the law who will be justified. 14 For when Gentiles, who do not have the law, by nature do what the law requires, they are a law to themselves, even though they do not have the law. 15 They show that the work of the law is written on their hearts, while their conscience also bears witness, and their conflicting thoughts accuse or even excuse them 16 on that day when, according to my gospel, God judges the secrets of men by Christ Jesus.
"You have no excuse..." Who has no excuse? Having dealt with the Gentiles, Paul shifts focus onto Jews who know the law, yet do not obey. Familiarity is of no benefit if it doesn't cause obedience.
Jews who fail to practice perfectly are just as guilty as sinful Gentiles apart from the law. Passing condemning judgement on others testifies to the knowledge of how a Jew should behave, though they do not. All are condemned; "there is none righteous..." but we're getting ahead of ourselves.
Conversely, how can those who follow Christ judge the unbelieving? Do they have the Spirit of God? Do you still practice that which He redeemed you from?