God never rules His people by giving them exhaustive lists of things they must do, and forbidding them to do anything else. He teaches them in general terms what pleases Him, and then He allows them to work out the specifics through their own godly wisdom, in line with the broader principles of His Word. That’s what it means to live according to divine prescription. Have I forgotten the “instructions regarding the tabernacle?” No, but note my term “exhaustive.” The directions for the tabernacle, elaborate as they were, were not exhaustive.God didn’t tell the artisans precisely what tree to use, in precisely what shape to make the noses of the cherubim, etc. He gave them general directions and let them work out the specifics according to their godly wisdom. John Frame
The fact that God favors some and passes by others, does not warrant the charge that He is guilty of injustice. We can speak of injustice only when one party has a claim on another. If God owed the forgiveness of sin and eternal life to all men, it would be an injustice if He saved only a limited number of them. But the sinner has absolutely no right or claim on the blessings which flow from divine election. As a matter of fact he has forfeited these blessings. Not only have we no right to call God to account for electing some and passing others by, but we must admit that He would have been perfectly just, if He had not saved any, Matt. 20:14, 15; Rom. 9:14, 15.Berkhof, L. (1938). Systematic theology (p. 115). Wm. B. Eerdmans publishing co.