Most pseudo-Christian sects & some denominations are based in misunderstandings of the Old Testament. In the New Testament we found the revelation of many things that were just shadows of Christ or a mystery in the Old Testament. People can find salvation & the simplicity of Christ by reading the New Testament alone, but that won’t happen by reading the Old Testament by itself.
Reformed/Calvinist theologians & Catholics teach the church is now ‘Israel‘ (Replacement Theology), but that’s NOT what the New Testament shows, please check in that link the 73 times the word ‘Israel’ is used int he NT. Also with some variations the Church of God & Hebrew Roots teach that Christians are ‘Israelites’.
These sects also teach Jesus only came to save the house of Israel by twisting Matt.15:24, & say for that reason we believers have to be Israel. But in the original Greek there is no word ‘only‘ neither the word ‘save‘:
” ὁ δὲ ἀποκριθεὶς εἶπεν Οὐκ ἀπεστάλην εἰ μὴ εἰς τὰ πρόβατα τὰ ἀπολωλότα οἴκου Ἰσραήλ” – (here or here)
The but answering [He] said, not I was sent, if not to the sheep – being lost of [the] house [of] Israel.