What is this business about a “sweet savour to the Lord” (Gen 8:21)?

This was not meant in any literal sense, considering that, not being essentially material, God had no need of food, he had no nose, etc. The smell of the sacrifice was probably not unlike that of delicious, savory food; the “sweet savour” thus describes how the sacrifice smelled to those offering the sacrifice. But, regardless of the smells wafting in the air to human noses, not every sacrifice was a “sweet savour,” because sin and trespass offerings did not have such a savor; while God required them, those sacrifices (symbolically, of course) smelled like sin to him. Hence the symbolic meaning of a sacrifice with a “sweet savour” is that the sacrifice was acceptable or welcome to God. This is plausible because Noah’s first activity upon disembarking was to sacrifice—his first thought was of God. It was not the scent of the meat but the performance of faithfulness that God enjoyed, and evidently, Noah was not making a sin offering for dead men; the dead were dead and no sacrifices for them were possible. These sacrifices were on behalf of Noah and his family, the living remnant. Indeed what follows this sweet-smelling sacrifice is “I will not again curse the ground any more for man’s sake” (8:21); and two verses later, beginning at 9:1, God blesses the remnant with man’s first laws and follows that with a covenant of divine peace. All was right with the world once again, for a short time.—Another common observation about “sweet savour” is that the root word rendered “sweet” is Hebrew נִיחוֹחַ, nichoach, glossed by Strong’s as “a quieting, soothing, tranquilizing”; hence it is said that the savor is actually a “savour of rest” (as Henry puts it). In this case, what the sacrifice metaphorically smelled of, to God, was not so much sweetness as restfulness. (It seems the Septuagint used ὀσμὴ εὐωδίας, which is where “sweet savour” came from.) Later uses of the phrase in connection to sacrifice are sometimes held to be allusions to this original “sweet” savor; the sacrifice gives spiritual rest to the penitent as Noah’s landing gave him rest from his yearlong peril. Thus Noah’s journey in the ark was not unlike that of Moses’ with the tabernacle: “My presence shall go with thee, and I will give thee rest.” (Ex 33:14)