by the power of the Spirit of God - “the Holy Ghost,” as the true reading seems to be. This seems intended to explain the efficacy of the word preached, as well as the working of the miracles which attested it.
so that from Jerusalem, and round about unto - “as far as”
Illyricum - to the extreme northwestern boundary of Greece. It corresponds to the modern Croatia and Dalmatia (2Ti 4:10). See Act 20:1, Act 20:2.