Messianic Judaism began as a movement for and by ethnic Jews, whereas the Sacred Name movement emerged amongst Gentiles. Messianic Judaism is therefore more likely to accept the views of traditional Judaism, such as not pronouncing the Tetragrammaton and keeping the Hillel II pre-calculated Hebrew calendar instead of sighting the New Moon (also see moon calendar). The Messianic Jewish mainstream sees nothing wrong with the existence of Gentile Christianity that does not keep Torah, whereas the Sacred Name Movement keeps Torah to their understanding of it.
Isaiah 56:6-7
The 613 commandments and their source in scripture, as enumerated by Maimonides:
Brother Sessiah Adams