In the Old Covenant, the Israelites were instructed to follow a lot of laws which included tithing. We are not taught to follow the rest of the laws they were given and neither should we try to follow the law of tithing.
The Israelites were asked to give what their hearts prompted them to give and on both occasions, the amount of gifts they gave was overwhelming.
In order for believers to be robbing God today, we would still have to be under all the laws God gave to the Israelites. The Bible tells us we are clearly not under those laws. In fact, the windows of heaven are not closed to Christians according to Ephesians 1:3 and 2 Peter 1:3.
Some say the tithing came before the law in an attempt to justify teaching it now. I'll show you that it is not a valid reason. Two incidents of tithing came before the law. Neither one is valid to use as justification that Christians ought to be 'tithing' now.
If we are taught to tithe in the New Covenant then there would be no issue. We are clearly not taught that we should tithe. Jesus told the Scribes and Pharisees that they should continue to tithe and keep all the other laws too! Jesus was not talking to us!
The things Jesus taught about money and what the rest of the New Covenant continues to teach is what we need to do today. Freewill gifts is the only way demonstrated in the New Covenant.
Hebrews chapter 7 is studied to determine what it really teaches concerning the law and concerning tithing. The conclusion is that it does not teach that Christians should be tithing and instead repeats what other verses also state - that Christians are not to attempt to follow the laws God gave to the Israelites.
I will add the more popular or difficult questions and answers to this on occasion.
We should be following the instructions outlined throughout the New Testament.
What should you do?
End of commentary.