It is a serious thing to question the love of God. Malachi message was the that God's people were in moral decline, including the priests. Paul warns Timothy (2 Timothy 3) about the last days. Moral decline is occurring even today. Malachi tells us about the growing dullness of God's people caused by the faithlessness of the priests.
God tells the priests that He will be honored, his name will be honored in all the earth. The priests have drifted far from God, no longer offering the proscribed sacrifices, instead offering blemished offerings. They also teach error in the temple. Even today, the clergy do the same, substituting a social gospel for the Gospel of Jesus