Some people claim that tithing is an eternal principle because Abraham gave one-tenth to Melchizedek before the Law of Moses.
People who follow this line of reasoning are inconsistent in their application of Scripture, because Abraham also sacrificed animals and kept the law of physical circumcision before the Law of Moses.
Does this mean that sacrificing animals and practicing physical circumcision are eternal principles which remain in effect in the New Covenant? No. Are believers required to sacrifice animals and practice physical circumcision just because Abraham practiced both of these things before the Law of Moses? No.
Animal sacrifices and the law of physical circumcision were brought to an end at Christ’s crucifixion, when the New Covenant was instituted by God through Jesus’ shed blood.
Just because the patriarchs practiced something before the Law of Moses doesn’t mean that it’s an eternal principle binding upon believers for all time. The patriarchs practiced many things that aren’t part of the New Covenant.
The phrase “eternal principle” means that a principle or law that God requires in all time periods, in all places, of all people. For example, “you shall not murder” is an eternal principle because all people, in all places, in all time periods are forbidden from taking innocent life. The same thing cannot be said of tithing.
God never required all people, in all places, at all times to tithe. God didn’t require anyone to tithe before the Old Covenant. And even during the Old Covenant, not all people were required to tithe (for example: Gentiles, the poor, widows, orphans, and people who weren’t farmers and shepherds weren’t required to tithe). This shows that tithing isn’t an “eternal principle.”
Even if we were to entertain the idea that tithing is an eternal principle, people who believe in tithing aren’t adhering to the tithing laws that God commanded in Scripture. They’re practicing a man-made tradition of monetary-tithing which developed after the original apostles died. So even if we go along with the idea that “tithing is an eternal principle,” it simply creates another problem which is. . . why isn’t anyone practicing tithing in the specific manner that God commanded in Scripture?
At any rate, Abraham’s tithe to Melchizedek doesn’t prove that tithing is an eternal principle, because God didn’t command Abraham to tithe to anyone and tithing wasn’t part of Abraham’s covenant with God. As believers in Jesus Christ, we don’t base our beliefs and practices on what Abraham did before the Law of Moses. We base our beliefs and practices on the full counsel of Scripture rightly divided through the illuminating light of Jesus Christ and the New Covenant.