Gratitude to Christ for his love and self-sacrifice may indeed be an effective motive to action, but faith in the efficacy of Christ's atoning sacrifice is no guide to conduct.
The inability of Protestantism to deduce a scheme of life from its own master-principle of salvation by "faith" has compelled it, in its desire to avoid the pitfalls of antinomianism, to revive in a modified form the practical legalism of the Old Testament.

The Protestant desires to show his gratitude to Christ by leading a correct life; but his distrust of his own higher nature compels him to go to some external authority for ethical guidance; and as he has repudiated the authority of the supernaturally-inspired Church, he is compelled to have recourse to the supernaturally-inspired Bible.
Hence the traditional alliance between Protestantism and the Old Testament, in which the path of duty is far more clearly and consistently defined than in the New.

And hence the singular fact that Calvinism, which is the backbone of Protestantism, and which in theory, and even (at times) in practice, regards "works" as "filthy rags," finds its other self in Puritanism, which is in the main a recrudescence of Jewish legalism in the more strictly _moral_ sphere of conduct.
It is owing to its alliance with the legalism of Israel, that Protestantism has been in some respects an even greater enemy of human freedom than Catholicism, and has on the whole done more than the latter to narrow and maim human life.

The strict legalist tries, as we have seen, to bring the whole of human life under the direct control of the Law; and when he finds, as the Puritan did in the sixteenth and seventeenth centuries, that whole aspects of life have in point of fact escaped from the control of religion and won from the latter a tacit acceptance of themselves as secular, he not unnaturally tends to regard these non-religious aspects of life as "carnal," and therefore as unacceptable to God.

Hence the antipathy of the Protestant, in his seasons of Puritanical fanaticism, to art, music, the drama, and other noble fruits of the human spirit.
Catholicism has found itself compelled to tolerate the secular activities of the layman; Protestantism, while tolerating those activities by which man earns his daily bread and which may be spoken of collectively as "business," has from time to time waged war against all the developments of human nature which are neither spiritual (in the narrow and rigid sense of the word) nor obviously useful, and has sought to extirpate the corresponding desires from the heart of Man.