NOTES for Mal 1:14
God gave us, for us, in expiation for our sins the best of what He had- Himself. And we are not even capable to trust Him. We generally don’t like to give something, not to talk of the best. Moreover we completely forget that this same "best" is given to us by God, it belongs to Him. So, returning it to God we lose nothing, but if we don’t return, then we are thieves. "sacrificeth unto the LORD a corrupt thing" - it is about us. Indeed, when we try to return to God, when do we ourselves give Him? He created us pure and beautiful, but we are completely different. But he can clean and forgive us, it will just be enough to sincerely ask Him for that.