The reason I believe that works are not required for salvation is because the scripture clearly teaches that one cannot be saved by mixing faith and works.
Rom.4: [4] Now to him that worketh is the reward not reckoned of grace, but of debt. [5] But to him that worketh not, but believeth on him that justifieth the ungodly, his faith is counted for righteousness. [6] Even as David also describeth the blessedness of the man, unto whom God imputeth righteousness without works,
There is nothing ambiguous about those statements.
Actually, the statements made in Rom 4:4-6 are "ambiguous" if, again, one does not realize that St. Paul is referring to the law of Moses when he speaks of "works" in this instance. This is where many who ascribe to sola fide run astray of the message of Sacred Scripture; when each instance of "works" is erroneously, automatically associated with any good works, not just the works associated with the law of Moses. IOW, when St. Paul speaks of "works" in all of his letters, sometimes he is referring to the "works of the law" (i.e, Mosaic law); sometimes he is referring simply to "good works". Rom 4:4-6 is referring to the former "works". It is the task of a student of Scripture to rightfully discern which kind of "works" St. Paul refers to at any given time.
Rom 4:13-15, "It was not through the law that the promise was made to Abraham and his decendants that he would inherit the world, but through the righteousness that comes from faith. For if those who adhere to the law are the heirs, faith is null and the promise is void. For the law produces wrath; but where there is no law, neither is there violation."
And...
Gal 3:8-12, "Scripture, which saw in advance that God would justify the Gentiles by faith, foretold the good news to Abraham, saying, "Through you shall all the nations be blessed." Consequently, those who have faith are blessed along with Abraham who had faith. For all who depend on works of the law are under a curse; for it is written, "Cursed be everyone who does not persevere in doing all the things written in the book of the law." And that no one is justified before God by the law is clear, for "the one who is righteous by faith will live." But the law does not depend on faith; rather, "the one who does these things will live by them". "
These passages, especially verse 12 of Gal 3, indicate that it is adherence to the law of Moses and the works associated thereof which St. Paul indicates are ineffectual for initial justification. Why? Because it is "grace through faith" (cf. Eph 2:8) that comes first, before works, but both are "done by them" (cf. Gal 3:12) eventually.
No one is initially justified by adherence to any law. On this actually Catholics do not disagree. Where we disagree with those who adhere to sola fide is that following faith, there must be good fruits produced, or else the "faith" is "dead". (cf Jas 2:26)