13For it is not the hearers of the law who are righteous before God, but the doers of the law who will be justified. - Romans 2:13
In the Reformed tradition, verse 13 has been described as a "hypothetical statement", stating that people can be justified by doing the law or having good works if they could only obey the law perfectly, but since no one can, the only option is to be justified by faith.
Evidence of Being in Christ
Rather than verse 13 being a "hypothetical statement", I believe this verse is describing a true Christian, who by the transforming power of the Holy Spirit will be a "doer of the law" or someone who will produce good works. It's important to note that I am not saying that works will merit or earn justification, but it will be the evidences of our union with Christ.
Piper and Wright Quotes:
John Piper states:
"I think that when Paul says, "doers of the law will be justified," he means that there really are such people, and they are the only people who will be acquitted at the judgment. This is not a hypothetical statement. It is a statement of actual, experienced fact. When Christ comes into a person's life by the power of the Holy Spirit through faith in the Gospel, that person becomes a "doer of the law." Not a sinlessly perfect law-keeper, but one who loves the law of God (= the law of Christ), and depends on God's help to live according to the truth (which now includes the cross of Christ and the work of the Spirit), and trusts God for his mercy when he stumbles (according to 1 John 1:9)." 
"Romans 2:13b says, "Doers of the Law will be justified." It does not say, "By doing works of the Law you will be justified." It simply says that the ones who will be justified are also those who are doers of the law. There is no causal connection asserted. So the verse is not a contradiction of Romans 3:20 which says, "By the works of the Law no flesh will be justified." There is nothing in Romans 2:13b that keeps us from believing in justification by faith alone. Faith is required by the Law, and faith is the sole means of union with Christ whose righteousness vindicates us at the judgment. All the other obedience that comes from faith is the fruit of that union, not the means of it. So Romans 2:13b is not a contradiction of Paul's teaching of justification by faith alone." 
 From Piper's sermon entitled "No Partiality with God" Part 2. See
N.T. Wright states:
"This passage has often been read differently. We heard yesterday that Augustine had problems with it (perhaps the only thing in common between Augustine and E. P. Sanders). That is hardly surprising; here is the first statement about justification in Romans, and lo and behold it affirms justification according to works! The doers of the law, he says, will be justified (2.13). Shock, horror; Paul cannot (so many have thought) have really meant it. So the passage has been treated as a hypothetical position which Paul then undermines by showing that nobody can actually achieve it; or, by Sanders for instance, as a piece of unassimilated Jewish preaching which Paul allows to stand even though it conflicts with other things he says. But all such theories are undermined by exegesis itself, not least by observing the many small but significant threads that stitch Romans 2 into the fabric of the letter as a whole. Paul means what he says. Granted, he redefines what ‘doing the law’ really means; he does this in chapter 8, and again in chapter 10, with a codicil in chapter 13. But he makes the point most compactly in Philippians 1.6: he who began a good work in you will bring it to completion on the day of Christ Jesus. The ‘works’ in accordance with which the Christian will be vindicated on the last day are not the unaided works of the self-help moralist. Nor are they the performance of the ethnically distinctive Jewish boundary-markers (sabbath, food-laws and circumcision). They are the things which show, rather, that one is in Christ; the things which are produced in one’s life as a result of the Spirit’s indwelling and operation. In this way, Romans 8.1–17 provides the real answer to Romans 2.1–16. Why is there now ‘no condemnation’? Because, on the one hand, God has condemned sin in the flesh of Christ (let no-one say, as some have done, that this theme is absent in my work; it was and remains central in my thinking and my spirituality); and, on the other hand, because the Spirit is at work to do, within believers, what the Law could not do – ultimately, to give life, but a life that begins in the present with the putting to death of the deeds of the body and the obedient submission to the leading of the Spirit."
 From Wright's talk entitled "New Perspectives on Paul". See http://www.ntwrightpage.com/Wright_New_Perspectives.htm