But if one of you suffers for being a Christian, let him not be ashamed; but let him glorify God in this matter.
True, Matthew's commission reveals Jesus commanding the apostles to "make disciples of all nations"  (Matthew 28:18-20); but that same commission reveals that all such disciples were to be "baptized into the name of the Father, and of the Son, and of the Holy Spirit."  The name "Christian" is the name of the Father in the sense of his having sent his only Son who is honored by the name; it is the name "of the Son," because of the word "Christ" which is the principal part of the name; and it is the name of "the Holy Spirit," because the Holy Spirit conveyed the name through Paul and Barnabas at Antioch in Syria.  One of the ways therefore in which Christians "put on Christ" in baptism  (Galatians 3:27) is by putting on the sacred name of "Christian" by the very act itself.