Thus, if tithing was before the Law then it should apply after the Law. Well, clear verses used above clearly state that tithing was of the Law. So, now we have to explain a situation, not a verse. The Bible doesn't say that Abraham was commanded to give a tithe. According to Bible dictionaries, tithing was popular among many nations.
History shows that many nations gave different percentages of their income for religious works.
The Lydians offered a tithe of their booty. The Phoenicians and Carthaginians sent a tithe annually to the Tyrian Hercules. These tithes might be regular or occasional, voluntary or prescribed by law. But, let's look at a similar principle to make a parallel. It is interesting to note that circumcision was given in the Law of Moses.