The Jesus part is just as much a part of shared faith as worshiping the same G-d as the Jews do, but the main difference in Christian and Messianic which I thought was spelled out in our SOF is that we believe the Torah to still be in effect that there weren't new holidays commanded but to celebrate the originals as well as Shabbat.
You can't say a Messianic is a Christian because you have to be able to reverse that to a Christian is a Messianic. Now to Jews who want to lump us all together they see us the same, however we do not and our SOF specifies that.
To wit
1. This is a Torah Observant forum where those in Judaism as well as the Gentiles who are coming to Messiah, and those who already know Him, may come and grow and learn more about a Torah observant life in Messiah. We advocate Torah Observance as part of our walk with Messiah Yeshua, since He is our example and was Torah Observant, along with the disciples. This can be an area of great division with much misunderstanding, so we must realize that we are all at different points in our walk and that the Ruach Elohim (the Spirit of God) will lead people to The Truth. We realize that not all Messianics have equal levels of Torah observance. The disputes concerning this matter will not be tolerated.
And
Please keep in mind that we consider Messianic Judaism to be a completely valid form of Judaismthat doesn't need the permission or affirmation from any other sect of Judaism to exist. Therefore, we don't believe it is necessary to convert to Orthodox Judaism or any other branch of Judaism to belong. Although there are different expressions of Messianic Judaism, as there are in other Judaisms, we believe Messianic Judaism; a Torah observant Judaism who believes Yeshua is the Messiah and believes the Apostolic writings hold authority, to be the true expression of Judaism that the scriptures and the God of Yisrael intended.
It doesn't say we are a form or branch of Christianity.