If I use Malachi 3:8-10 to preach tithing then am I a minister of the New Covenant?

Is this putting law on my brother or sister? Will this law empower the "old nature"? Where is evidence in the book of Acts concerning tithing? Do I really owe God? If I don't then why does the preacher say I'm robbing God? I thought Jesus paid it all. Did He or didn't He?