Perhaps the significance of those things, in the inward fat, meaning the prime parts of the animal, was meant to show that all offerings to the LORD must be from the heart, including the best of our affections. Proverbs 23:26.
Related Commentaries of Leviticus 3:3
Leviticus 3:3-5
3 And he shall offer of the sacrifice of the peace offering an offering made by fire unto the LORD; the fata that covereth the inwards, and all the fat that is upon the inwards,
4 And the two kidneys, and the fat that is on them, which is by the flanks, and the caulb above the liver, with the kidneys, it shall he take away.
5 And Aaron's sons shall burn it on the altar upon the burnt sacrifice, which is upon the wood that is on the fire: it is an offering made by fire, of a sweet savour unto the LORD.