The author of the book of Ephesians is declared in the first verse of the book itself, “Paul an apostle of Christ Jesus.”
Also note it tells that Paul is “an Apostle of Christ Jesus.”
Paul wrote Colossians as well as Ephesians. We see Colossians 4:7-8 directly corresponds with Ephesians 6:21-22. Both Scriptures refer to Tychicus as the messenger to both churches. This implies that both books were written almost at the same time, by the same author, and possibly sent to each church close to the same time.
During this time Paul was imprisoned. His imprisonment was in Rome which establishes the reason for Tychicus as the messenger.
Some more recent scholars would argue that Paul is not the Author of Ephesians due to dramatic differences in the style of other Pauline epistles in comparison to Ephesians. The other books he wrote such as Romans, Galatians or Philippians all have specific tones or controversial elements. Philippians has an encouraging tone, Galatians has a difficult tone, and Romans has a tone in which arguments and misrepresentations of the Roman church are brought into the open. In Ephesians there seems to be no controversial element which makes some recent scholars question its authorship.
One would assume that Paul was writing this letter to Ephesus simple due to the title of the book. This however, is not the case. The scribes of the second century are the one who labeled the epistles with their current names. Philippians and Corinthians were easier to pinpoint because the recipients are mentioned directly. With these two books we can assume that the title is correctly implemented due to the specific mentioning of the intended audience. In Ephesians this is not the case. No where in Ephesians do we see the audience pinpointed at Ephesus, that is, in the original text.
So we can infer from this that Paul may not necessarily be writing specifically to the Church in Ephesus but rather to the entire church in Asia. The idea that this letter is not as specific as the others may help prove the generality of the region for which it is intended. It also proves that the drastically difference in tone does not negate its authorship.
We have already established that that Ephesians was most likely written at the same time as Colossians. Another book was written close to the same time. In 63 A.D. three scrolls of papyrus were takes from Rome to Asia. These three were prison epistles known as Ephesians, Colossians, and Philippians.
One of the main purposes of the book of Ephesians is to reconcile the Gentiles to God.
Since this book had no greeting of specific individuals and was strangely general we can conclude that this letter was meant to pass from church to church.
We can see that since this book was written to the Gentiles in Asia it would be focusing mainly on bringing Gentiles into the body and teaching them the ways of Christianity.