II. … For as there are two covenants which God willed to make with men—legal and evangelical. Accordingly there is also a double justification or a double method of standing before God in judgment—legal and evangelical. The former consists in one’s own obedience or a perfect conformity with the law, which is in him who is to be justified; the latter in another’s obedience or a perfect observance of the law, which is rendered by a surety in the place of him who is to be justified—the former in us, the latter in Christ. Concerning the first, Paul says, “Not the hearers, but the doers of the law shall be justified” (Rom. 2:13); and “Moses describeth the righteousness which is of the law. That the man which doeth those things shall live by them” (Rom. 10:5). Concerning the other, he says, “The gospel is the power of God unto salvation to every one that believeth, for therein is the righteousness of God revealed from faith to faith: as it is written, The just shall live by faith” (Rom. 1:16, 17); and “Being justified freely by his grace through the redemption that is in Christ Jesus” (Rom. 3:24). Concerning both, he says, “That I may be found in Christ, not having my own righteousness, which is of the law, but that which is through the faith of Christ” (Phil. 3:9; cf. also Rom. 9:30, 31). Hence a twofold justification flows: one in the legal covenant by one’s own righteousness according to the clause, “Do this and live”; the other in the covenant of grace, by another’s righteousness (Christ’s) imputed to us and apprehended by faith according to the clause, “Believe and thou shalt be saved.” Each demands a perfect righteousness. The former requires it in the man to be justified, but the latter admits the vicarious righteousness of a surety. The former could have place in a state of innocence, if Adam had remained in innocence. But because after sin it became impossible to man, we must fly to the other (i.e, the gospel), which is founded upon the righteousness of Christ. [Francis Turretin, Institutes of Elenctic Theology, 2.16.II.2]
We notice here that Turretin holds to the strongest version of the Law-Gospel distinction. Note also the proof texts Turretin utilizes, which are the texts that those of us who hold to the Law-Gospel distinction have likewise used to support our position. Romans 2:13 was appealed to to speak of the principle of the covenant of works, not as how some contemporary theologians have interpreted as speaking of spirit-filled obedience.
It is thus Reformed to speak of justification by works. The question is not whether we are justified by works, but whose works. The Reformed position is that we are justified by Christ's work, not ours. Christ did everything, and then imputed his righteousness to us through faith. Therefore, believers' justification is through faith because of Christ, and thus the Gospel is one where no one can merit salvation even one bit.