That is a very interesting observation and question. Let’s read Genesis 14:16-20 and then we’ll try to answer your question. “So he (Abraham) brought back all THE GOODS, and also brought back his brother Lot and his goods, as well as the women and the people. And the KING of Sodom went out to meet him at the Valley of Shaveh (that is, the King’s Valley), after his return from the defeat of Chedorlaomer and the kings who were with him. Then Melchizedek king of Salem brought out bread and wine; he was the PRIEST of God Most High. And he blessed him and said: ‘Blessed be Abram of God Most High, Possessor of heaven and earth; and blessed be God Most High, Who has delivered your enemies into your hand.’ And he (Abraham) gave him (Melchizedek) a TITHE of all” (NKJV).

In this short and rather abrupt account of Abraham’s victory in war and his encounter with Melchizedek we have the FIRST MENTION OF A PRIEST and the FIRST MENTION OF A TITHE being given. Are they related? I have no doubt that they are. As you intimated, tithes were also given under the Law. Who were the tithes given to under the Law? Ah, they were given to support the Levites, who were the PRIESTS in Israel. “For THE TITHES of the children of Israel, which they offer up as a heave offering to the LORD, I HAVE GIVEN TO THE LEVITES AS AN INHERITANCE; therefore I have said to them, ‘Among the children of Israel they shall have no inheritance’” (Number 18:24). As you may know, it was among the tribe of Levi that God set up the priesthood and in order to support their work in His sanctuary they were given tithes “as an inheritance.” So, simply put, I believe TITHES are related to the PRIESTS and because Melchizedek was a PRIEST Abraham acknowledged him as such and “gave him a TITHE of all.”

Is this a principle for us to follow? If you read through all of the New Testament you will only find the word “tithe” twice. It is found in Matthew 23:23 and Luke 11:42 and in both cases it is speaking to those who were still “under the Law” where the Levitical priesthood was still in place. From Acts through Revelation it is not mentioned once, for the Old Covenant of Law with its priesthood was replaced by the New Covenant of Grace which has made every believer a priest. “Coming to Him (Jesus Christ) as to a living stone, rejected indeed by men, but chosen of God and precious, you also, as living stones, are being built up a spiritual house, a HOLY PRIESTHOOD, to offer up spiritual sacrifices acceptable to God through Jesus Christ” (1st Peter 2:4-5). Thus there is no “special class of priests” in the Church of God; we are ALL PRIESTS who are privileged to function as worshiping priests before God.

Having said that, there are those in the Church who have been called and given special gifts to labor in the Word (by preaching the gospel to the lost and teaching the Word to the saints…see Ephesians 4:7-8, 11). Because these men give up their livelihood to devote themselves to full-time ministry in the Word, other believers should support them with monetary gifts. Yet it is not a LAW but an APPEAL by God for us to minister unto them in a “material way” because they have ministered unto us in a “spiritual way.” We see this principle brought out in 1st Corinthians 9:11, 13-14, “If we have sown SPIRITUAL THINGS for you, is it a great thing if we reap your MATERIAL THINGS?…Do you not know that those who minister the holy things eat of the things of the temple, and those who serve at the altar partake of the offerings of the altar? Even so the Lord has commanded that those who preach the gospel should live from the gospel.”  It is also not called TITHING, for in tithing one gave 10% of their goods to the Lord to meet various needs where today believers are encouraged to give “As God has prospered him” (1st Corinthians 16:2). It “may” be 10%, but it may be much more, or it may even be less. And last, but not least, we are giving because we WANT TO GIVE, not because we HAVE TO GIVE. And thus, we read in 2nd Corinthians 9:7, “So let each one give as he PURPOSES IN HIS HEART, not grudgingly or of necessity; for God loves a CHEERFUL GIVER.”  (439.1)  (DO)