Messianic Judaism, largely, finds it's historicity in Protestantism, with the trappings of medieval rabbinic Judaism, a defunct religion that lacks the means by which to propitiate sin (lack of the temple).
Orthodox Christianity finds it's historicity in Christ Himself through the Apostles and maintains the sacrifices of the Old Covenant as fulfilled by the sacrifice of Christ and entered into at each Liturgy. Furthermore, the Scriptures are read and praise is offered to God during the Liturgy of the Word prior to the Eucharistic offering. It is the historic continuance of Old Testament Judaism, both of the Temple variety and the synagogue variety.
Messianic Judaism being based on the Jewish trappings of the Middle Ages means they also lack the continuance of the Temple sacrifices and are defunct. What's worse is that their traditions are based off of those Jews who rejected the Christ, and therefore are in many ways like those who St. Paul describes as olive branches broken from the tree (Romans 11:17) and who our Lord Himself described as "withered" (John 15).
In short, Orthodox Christianity is the sacramental and historical continuance of the religion of the Old Testament. Messianic Judaism, on the other hand, is a Protestant anachronism based off of medieval Judaism that is cut off from the Temple, unable to offer sacrifices, and has rejected the Christ.
Expound on that with him.