What the Bible says about Received as an Angel of God
(From Forerunner Commentary)
Paul calls to their mind their first encounter with him, when his physical infirmity could have been a social stumbling block for them, but they received him warmly and without hesitation. He is drawing a contrast between their first meeting and their current rejection of his teaching.
Paul says that they received him "as an angel [messenger] of God." In the beginning of the epistle, part of his stern warning was against any other doctrines from what he had originally taught them, which included a warning against the teachers of such doctrines (Galatians 1:8). Since the Galatians "received [him] as an angel," they may have likewise received a false teacher as a messenger from God and bestowed upon him the same warmth and acceptance.
David C. Grabbe