After having just blessed his audience with grace and peace from God the Father and the Holy Spirit (called here "the seven spirits"), John adds in the first part of verse 5:
and from Jesus Christ the faithful witness, the firstborn of the dead, and the ruler of kings on earth.
Just as grace and peace come from the Father and from the Holy Spirit, they also come from Jesus Christ, the Son of God, the second person of the Godhead. He is described here as "the faithful witness." As we mentioned when we looked at verse 1, this book is a revelation of Jesus Christ. It was given to Him by the Father, but Jesus is the One who (through an angel) delivered it to John. Jesus is the faithful witness of His Father. His ministry was to reveal the things that His Father sent Him to reveal, and that continues even now in the book of Revelation.
Jesus is also "the firstborn of the dead" (v. 5). A great hope that Christians have is that though they will one day die, if the Lord tarries, they will later be resurrected. And the reason we can have unshakeable confidence in that is that Jesus Christ was the first to be resurrected unto eternal life. Because He has risen, we know that we, too, will rise.
He is also "the ruler of kings on earth" (v. 5). He is the king of kings. All serve His purposes now, whether they realize it or not. And all will one day bow the knee to Him.
This is our faithful and glorious Christ. And it is from Him, together with the Father and the Holy Spirit, that we receive grace and peace.