The question you have raised is not my area of expertise, but the Norman Willis' theory is on the one hand, speculation, and on the other, a veiled attempt to exalt the Old Testament and the Old (Mosaic) Covenant above the New. The Book of Hebrews was written to dispute folks like this, by constantly showing how Christ and the New Covenant was "better" than the old.
To my knowledge, it is almost universally accepted that Jesus and His disciples spoke in Aramaic. The theory that the New Testament was written in Hebrew is without basis, though I believe that I have heard some suggest that some of the sources may have been in Aramaic. The simple fact is that the Jews lost their facility in Hebrew. That is why the Old Testament had to be translated into the Greek language (this translation is known as the Septuagint). You will remember that when Jesus cried out from the cross, "Eli, Eli, LAMA, SABACHTHANI"(Matthew 27:46-47). Jesus was citing the Hebrew text of Psalm 22:1, and no one there seemed to understood it. They thought Jesus was calling for Elijah. How could this fellow’s theory hold up if no one at the cross could understand the Hebrew words Jesus spoke. (Hebrew and Aramaic are related languages, but not the same.)
Our Lord came, not to abolish the law, but to fulfill it (Matthew 5:17). He lived a perfect life, under the law, so that His sacrificial death would pay the penalty for our sins, and not His own. His death instituted the New Covenant (Luke 22:20) which was foretold in the Old Testament (Jeremiah 31:31).
Notice that this fellow's conclusions are reached without evidence (there are no Hebrew manuscripts of the New Testament books, only Greek manuscripts). He uses phrases like, "I starting thinking about it. . . something didn't add up" and "I began to wonder. . ." and so on, indicating that all of his theories originated in his own mind. I did not have the time to read all of his words carefully, but I did not see him quote any respected scholarship.
The New Testament gives us many warnings about the Judaisers – those who wish to bring us back under law, rather than under grace. Galatians is the strongest indictment against this heresy. But Paul often warns about Jewish speculation and myth (see 1 Timothy 1:3-7; 6:3-5; 2 Timothy 2:14-26; 4:2-4; Titus 1:9-14).
Mr. Willis starts by saying that he was taught certain things, all of which were justified by the fact that the New Testament was inspired and written in Greek. I have never heard this argument before. He is seeking to refute Christian doctrine on the basis of some falsehood that he heard. In Romans 9-11 we find the inspired version of the relationship of Jews and Gentiles in the program of God (especially chapter 11). The same subject is addressed in Ephesians chapter 2. Mr. Willis should give special attention to Paul's view of his "Jewish good works" in Philippians 3:1-16, especially verses 7-10.
Mr. Willis' words are so filled with error that one could spend countless hours refuting his every point. I don’t have the time, so let me give you an example, which seems to suggest that Mr. Willis is not really a student of the New Testament. His statements regarding the New Testament seem second-hand:
The "gentiles" and "Greeks" that we have always been told that Sha'ul's was sent to minister to were in actual fact Diaspora Israelites of the Northern Kingdom of Israel (the Lost Ten Tribes), and the Hellenized Jews of the Diaspora and the Babylonian Exile, respectively. They are not the same as what we in Christian culture think of as Greeks and gentiles at all.
I looked up every reference to "Gentiles" in all four Gospels and Acts. Not one time was "Gentile" used for a Greek speaking Jew. Look at these instances, where Gentiles are contrasted with Jews:
The arguments he puts forth reveal a gross ignorance of the New Testament, and should not be taken seriously.
Willis spends a great deal of time trying to convince his reader that the New Testament was not written in Greek, but in Hebrew. That's false, but so what? His real heresy is his denial of the gospel:
As long as we get it in to our heads that Yahshua came not to replace Israel and the Torah, but to show people how better to keep the Torah, then we have a chance of getting it right. He came not to replace what He Himself handed down to Moses in the Wilderness, but to clarify it. Otherwise, when Yahshua, Moses and Elijah (Eliyahu) were all standing there together in the transfiguration on the Mount of Olives, talking amongst one another, why did Yahshua not rebuke them for teaching the wrong thing?
In other words, Jesus came to show us how to better keep the law. In the Sermon on the Mount, Jesus showed that keeping the law of Moses was impossible. In Romans 3 Paul concludes that law-keeping can save no one, for we must keep the whole law, without violating one point (see James 2:10 as well). Paul shows us that the law cannot save anyone; it can only condemn us (Romans 3:9-20). Apart from the Law, the righteousness of God was manifested in Christ. It is His sacrificial death for our sins that saves us, and not our efforts to keep the law.
Willis' bottom line is wrong, dead wrong; heresy.
It is that simple.