My son was raised in the church. He recently started "keeping the Sabbath," and is taking my three grandsons to a motel where they have a private church -- just the four of them. They study the word with a group on the Internet!
He will not go to church, nor let his sons go with me to Sunday school. In fact, they can't do anything with me on Saturday anymore!
Of course, all of this has me concerned, yet I have no influence over him. I am wondering if he has been brainwashed. Could this be a cult?
Your son has been caught up in one of the many Messianic Jews groups. The best way to describe them is to think about the Judaizing teachers Paul battled in the New Testament and realize that their false doctrine has been resurrected.
One of the common features of these groups is the idea that there is one set of laws for the Gentiles, but the Jews are to continue keeping the Old Testament. Since these people want to keep the Old Testament, everyone tries to "prove" they have some sort of Jewish lineage. I looked at the web site you sent me and the writer is a classic instance of this, claiming to have "lost" his true last name because his maternal grandfather changed his name when he came over to the United States. Whatever happened to his father's name is never mentioned. But he "discovered" that he supposedly ancestors with Jewish sounding names.
Another feature is the refusal to use the name Jesus. Yeshua is the claimed name of Jesus, a transliteration of Joshua from the Hebrew. This is because Messianic Jews claim the New Testament was originally written in Hebrew and then translated to Greek. Our name "Jesus" is derived from the Greek. The fact that New Testament Greek shows no signs of being a translated work and that there are no Hebrew New Testament writings predating the Greek doesn't matter to this group. The Hebrew translations do read just as you expect -- Hebrew translations of Greek writings.
It isn't a cult. Cults revolve around a single dynamic individual. This man claims not to have started a new religion, but has been ordained a minister by another Messianic Jewish group. This is just one of many diverse Messianic Jewish groups.
Why someone would be interested in this man's teachings is beyond me. He doesn't write well in English, so I have a hard time believing he is as knowledgeable in Hebrew as he claims. He is simply a false teacher trying to establish a congregation. I'm sorry your son is fooled by him. But handle this like any other false teacher. Challenge him to prove his points by the Scriptures. And then show him from the Bible that he isn't following God.
"For the weapons of our warfare are not carnal but mighty in God for pulling down strongholds, casting down arguments and every high thing that exalts itself against the knowledge of God, bringing every thought into captivity to the obedience of Christ" (II Corinthians 10:4-5).