Let’s suppose you left your wallet on your seat and I found it tomorrow. Because I found it I instantly believe I have a right to entitlement and spend the money that you have in your wallet (or use your credit cards!) When you find out I did that you will rightfully be angry and accuse me of stealing from you. You will argue that because I held your resources in my hands did not give me entitlement to help myself to it.
The Lord's tithe operates on the same principle. His money is in amongst the income we generate because it all belongs to him. He outlined that of our resources a minimum 10% of those resources are to be set aside for the work and needs of the church. What happens sadly is we open his wallet and say, “I’ll take that.” It's stealing