Jesus Christ sent His disciples, on His own explicit instructions in Matthew 10:6, "To the lost (Apollumi) sheep of the house of Israel." And that is exactly where they went.
That the Jews are not the "sheep" of the "house of Israel" is made clear in John 10:24, "Then came the Jews round about Him, and said unto Him, How long dost, thou make us to doubt? If thou be the Christ, tell us plainly. Jesus answered them, I told you, and ye believed not, the works that I do in My Father’s Name, they bear witness of Me. But ye believe not, because ye are not of My sheep, as I said unto you. My sheep hear My voice, and I know them, and they follow Me." A plain interpretation of that would be that Christ said His Israel sheep would follow and believe in Him, i.e., become “Christians.”