“10 So shall your barns be filled with plenty, and your presses shall burst out with new wine. (The word “firstfruits” speaks of the tenth, and, therefore, tithing. Tithing is carried over into the New Testament, as well. The Melchizedek Priesthood is eternal and must be supported by the children of Abraham, which include every Believer [Heb. 6:20; 7:1-11].)”
Excerpt From
The Expositor's Study Bible
Jimmy Swaggart
https://books.apple.com/us/book/the-expositors-study-bible/id399697870
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Swaggart is simply wrong on these issues.
The passages that lay out the requirements for tithing are not those that address firstfruits. The two are distinct.
Tithing (under the Law) is addressed in four places: Leviticus 27, Numbers 18, Deuteronomy 12, and Deuteronomy 14. None of those passages discuss firstfruits.
Firstfruits (as an offering) is addressed in many places, but only twice in Scripture is it mentioned alongside "tithing"; in 2 Chronicles 31:5, where "tithe" seems to indicate amount rather than legal requirement; in Nehemiah 10:37, where they are clearly distinct, and in Nehemiah 12:44, where they are mentioned together, but not conflated, again making them distinct.
Nowhere in Scripture are "firstfruits" directly identified as "tithes" or vice-versa.
As for the passage in Hebrews, it says
absolutely nothing about supporting the church through tithing. It says
absolutely nothing about a requirement for tithing under the new covenant. It says
absolutely nothing about supporting the eternal priesthood at all.
It is clear that Mr. Swaggart is teaching a false message here.
Maybe you should stop promulgating his errors.