Why it does not matter. It mattered all the time, even when Jesus was preaching.
i will tell you why it does not matter what Jews believe
now.
the first Christians were Jews. These Jews, because of Jesus, became Christians and held different beliefs yet there remained a portion of Jews who did not believe in Jesus, and hence they are still Jews.
that’s number 1.
Number 2, Jesus came to reveal about God and His plan and His New Covenant with humanity. If Jews did not even recognize their Messiah, what makes you assume they have complete knowledge of God? without the belief in Jesus, there is no Christianity and Christianity is what Jesus taught, so if Jews do not believe in Jesus, they will not believe that He is the Word incarnate, so they will not focus on the Word of God, but this does not mean that Jews do not believe that the Word of God= God. Jews simply do not believe that Jesus is the incarnate Word of God. It is a chain of belief related to who Jesus is. If they don’t believe in Jesus, of course they won’t believe in the Word that took a human flesh, neither in the New Covenant that replaces the Old one.
It matters now too. The Jews have a religion and because your religion is emanating from the Jews, because Jesus himself was a Jew, his mother Mary was a Jewess and all disciples (except perhaps John) were Jews. The christionas are keeping attachment with the OT. So it matters very much as how church can take a totally different line from the Jewish religion in the matter of Trinity etc.