Revelation 1:4

4 John to the seven churches which are in Asia: Grace be unto you, and peace, from him which is, and which was, and which is to come; and from the seven Spirits which are before his throne;

The book was written to seven churches in Asia. There were many more churches than just these seven in the world and in Asia. The churches picked were not even the most prominent churches of John's time. These seven churches were picked because they had specific traits that Jesus wanted to address. Those seven churches represent the seven types of assemblies and the individuals within them that identify with Christianity throughout the entire new covenant Church age on earth. This age is from Pentecost until the marriage in heaven.

John announces grace to the Church and peace from Him which is, which was and which is to come. This person giving the greeting is not Jesus because Jesus is seen separately in the next verse. It can only be Father God giving the greeting and what is said there can be equated to saying that He is the one that exists, He Has always existed and He will always exist.

There are seven Spirits before his throne. The names of the seven aspects of the Holy Spirit are given in the book of Isaiah.

Isaiah 11:2 And  the spirit of the LORD shall rest upon him, the spirit of  wisdom and  understanding, the spirit of  counsel and  might, the spirit of  knowledg e and of  the fear of the LORD ;