In logic we sometimes talk about "sufficient" and "necessary" conditions. A condition is considered necessary if it must occur in order for something to be true. For example, the presence of oxygen is a necessary condition for human life. Without oxygen humans could not live, and therefore the presence of oxygen is a necessary condition for human life.
A sufficient condition, on the other hand, doesn't have to exist for something to occur, but if it does, the event must occur. For example, the absence of oxygen is a sufficient condition for human death. Of course human death could occur for other reasons, but the loss of oxygen is a sufficient condition for it to occur.
Most of the time we can't identify the complete set of conditions that would suffice for an event or circumstance, though we often can determine what's necessary. For example, though oxygen is necessary for human life, it is not by itself sufficient, since humans also need water, food, brainwave activity, and a number of other conditions in order to live. In other words, while it's necessary for human life to have oxygen, it's not sufficient. To state this more formally, if X is true (human life), then Y must be true (oxygen must be present). The presence of Y (oxygen) is therefore necessary for human life (Y) - though (again) oxygen (Y) is not by itself sufficient to guarantee human life (X).
Applied to the realm the spirit, I want to make the case that if there is genuine life (X), then there must the presence of a Jewish heart (Y) operating in the life of the believer. In other words, the presence of a Jewish heart is necessary for true life in the spirit. If you are a "Christian" (i.e., a follower of the Jewish Messiah), then you must have a Jewish heart; i.e., having a Jewish heart is necessary for being a Christian. You simply can't be a genuine follower of Yeshua without such inward teshuvah.
Note, however, having a Jewish heart (Y) by itself is clearly not sufficient for being a Christian (X), no more than the presence of oxygen is sufficient for human life. Many people that have a Jewish heart clearly reject Yeshua as the Messiah. (Go to any Orthodox synagogue or attend a seminar at your local Jewish Community Center and you will find many Jews who truly have Jewish hearts but who are not followers of the Messiah Yeshua.) So while it's true that having a Jewish heart is not sufficient for being a Christian, it's a necessary consequence... One implication of this is that it is impossible for someone to be a true Christian and yet be an "anti-Semite" or hater of the Jewish people. This only makes sense, of course, since followers of Yeshua are "circumcised in the Spirit" (Rom. 2:29; Col. 2:11) and grafted into the covenantal promises and blessings originally given to the Jewish people (Rom. 11:17-24). A true Christian, in other words, will be "Jewish" in the spiritual sense (Rom. 2:29). If you are Messiah's, you are a spiritual Jew; and by contraposition: if you are not a spiritual Jew, you are not a Christian.
I write all this because I am often both mystified and perplexed that many people who consider themselves Christians do not embrace their Jewish heritage and identity. (Sadly we recently left a Church we had been regularly attending for years because of the refusal of the leadership to accept this basic truth.) I am even more distressed whenever I hear so-called Christians speak in anti-Semitic terms or who regard "Jews" as "Christ killers," etc. This sort of ignorance and hatred is diametrically opposed to the mission of Yeshua, who was born the King of the Jews and who came for the lost sheep of the House of Israel (Matt. 2:2; 10:5-6; 15:24).
It is important to think clearly about all this, chaverim, but I am concerned that much of the contemporary Church has been so brainwashed by Gentile prejudice and tradition that it cannot apprehend its indebtedness to the Jewish people. Gentile Christians are "grafted in" to the covenants, blessings, and future of the Jews, not the other way around. The Olive Tree metaphor given in the Book of Romans makes this clear. Tragically, Christians rarely give the Jewish roots of their faith a second thought, or at best consider it a trifle, a curiosity, or even a novelty -- like attending a 30 minute cartoon presentation of "Christ in the Passover" or some such thing. Look -- understanding the Jewishness of Jesus and the Jewish roots of Christianity should not be regarded as adding some "ethnic spice" to otherwise "Goyishe" ways of thinking; on the contrary, such constitutes the essential truth of your identity in the Jewish Messiah. Yeshua will one day return to Jerusalem to establish the Millennial Kingdom to fulfill the promises made to ethnic Israel. And beyond this, in the eternal state to come, the gates of the "Heavenly Jerusalem" will be inscribed with the names of the 12 tribes of Israel. Jewish identity is not an accident of the spirit, but a necessary part of being part of the family of God.... Take hold, chaverim!