Here, Do Nothing Nor Render Anything To God...

Evangelista: No, indeed; none of Christ's are to have anything to do with the covenant of works, but Christ only. For although in the making of the covenant of works at first, God was one party, and man another, yet, in making it the second time, God was on both sides: God, simply considered in his essence, was the party opposed to man; and God, the second person, having taken upon him to be incarnate, and to work man's redemption, was on man's side, and takes part with man, that he may reconcile him to God, by bearing man's sins, and satisfying God's justice for them. And Christ paid God till he said he had enough; he was fully satisfied, fully contented, (Matt 3:17), "This is my beloved Son, in whom I am well pleased." Yea, God the Father was well pleased, and fully satisfied from all eternity, by virtue of that covenant that was made betwixt them. And thereupon all Christ's people were given to him in their election. (Eph 1:4) "Thine they were," says Christ, "and thou gavest them me," (John 17:6)... 

So that all the covenant that believers are to have regard to, for life and salvation, is the free and gracious covenant that is betwixt Christ [or God in Christ] and them. And in this covenant there is not any condition or law to be performed on man's part, by himself; no, there is no more for him to do, but only to know and believe that Christ hath done all for him...

I beseech you to be persuaded that here you are to work nothing, here you are to do nothing, here you are to render nothing unto God, but only to receive the treasure, which is Jesus Christ, and apprehend him in your heart by faith, although you be never so great a sinner; and so shall you obtain forgiveness of sins, righteousness, and eternal happiness; not as an agent but as a patient, not by doing, but by receiving. Nothing here comes betwixt but faith only, apprehending Christ in the promise. This, then, is perfect righteousness, to hear nothing, to know nothing, to do nothing of the law of works; but only to know and believe that Jesus Christ is now gone to the Father, and sitteth at his right hand, not as a judge, but is made unto you of God, wisdom, righteousness, sanctification, and redemption."

Edward Fisher, The Marrow of Modern Divinity

In a word, from the Westminster Shorter Catechism:
Q. 86. What is faith in Jesus Christ?
A. Faith in Jesus Christ is a saving grace, whereby we receive and rest upon him alone for salvation, as he is offered to us in the gospel.