Walk in a manner worthy of the calling with which you have been called... That sounds like an instruction to live up the standard we have attained in Christ...  Looking at Ephesians 4:1 more closely we find that's not at all what Paul is instructing the church in Ephesus.  We discover that what he is asking is that the church relate to one another on the basis of the grace (the calling or invitation) shown to each one which has already been given a new name and identity ("you have been called").  Treating one another based on our individual identities in Christ rather than based on performance, is a next step to recognizing the truth of your own identity in Christ.