Sefer Avodas Yisroel translates the word "v'ashamartem" to mean "to wait" (as in Bereishis 37:11). Accordingly, the pasuk is saying that one should wait for and anticipate the bris and constantly ask when he will merit to create a genuine covenant with his Creator.
He adds that there are many people who desire to serve Hashem but they are caught up in their earthly pursuits and don't end up doing it. Therefore, the pasuk stresses to "do them". This teaches us that merely anticipating the covenant is not enough. One also must do his part by completely immersing himself in avodas Hashem. If one does this, he will "succeed in all that he does."