Verse 4 of chapter 1 brings about the original opening of the letter as John introduces himself as the writer and the 7 churches as the recipients. He then moves into a formula that also can be seen in many of Paul's letters as he offers grace and peace to those who are reading/hearing the letter.
This though is not just an opening gambit, it also sets up the theme of the whole letter. John in these opening words uses well worn Roman phrases and ideas for YHWH to show his authority over that of the Empire. The grace and peace that John offers in God's name is set against the Pax Romana (peace of Rome) that the churches this letter is written to would have been well aware of.
The next phrase which is seen in a number of forms throughout the letter is also a play on a formula used of Roman deity's. Who is, and who was, and who is to come, sets out the eternal nature of God and is similar to phrases used of Zeus and other Roman god's.
The seven spirits or sevenfold spirit before his throne speaks of the fullness and completeness of the Holy spirit at work in the world. Finally we have the mention of Jesus along with a number of titles which again give him authority over all others. He is the faithful witness to who God is, the first born of the dead opening the way to eternal life for all people having defeated sin and death and finally he is the ruler of the kings of the earth including the Roman emperor.
We can see in this introduction two things, one is that of John setting up the God of these 7 churches over and against the power of Rome. John wants these churches to know from the beginning that although it may look like Rome is in power actually God the Father, Spirit and Son are.
The second point is something that didn't become Christian doctrine till hundreds of years after Jesus died and that is that of the trinity. Although I don't want to go into great detail here about the ins and outs of this belief I want to flag up that here John is very clear in his recognition of the Father, Spirit and Son.
