God Cares About How You Worship, Pt. 2

IV. They showed their irreverence by their attitude in worship (vv. 12, 13a).
In short, they show contempt towards their sacrifices and their attitude showed their disgust and weariness!

V. They showed their irreverence by their cheating God in worship (vv. 13b, 14a).
God does not say, "Your intentions were good; I don't really need that." He says, "Cursed be the cheat…" God did not ask for the specific sacrifice but if they vowed it, they must keep it. It was not a promise given to a mere mortal but to the living God. God will not be cheated. We can cheat people and no one may ever know and we could die without ever being discovered. But not with God.

VI. They showed their irreverence by what they taught (2:1-9).
God's covenant with Levi, the priesthood given to them, required that they instruct God's people (v. 6) and turn God's people away from iniquity (v. 6). They spoke in behalf of God (v. 7) and therefore people should listen to them. We read in the Pentateuch repeatedly that after specific commands were given in the matter of sacrifices, building the tabernacle, etc. that they did everything the Lord had called them to do. After coming into the promised land, that kind of verdict began to disappear and we learn early on that the sons of Eli were wicked priests. That wickedness continued in the post-exilic priests.
But, instead of turning many away from iniquity (v. 7), they "caused many to stumble by" their instruction. In return, God would make them despised and abased before the people. In short, by not teaching God's people faithfully, they brought condemnation upon themselves.