To the seven churches do not mean there were only seven churches in the Roman province of Asia. Instead, these seven churches represent the entire group. "Grace and peace" is a typical Christian greeting (see study notes on 2 Corinthians 1:1–2; 2 Thessalonians 1:1–2). The order of these words is consistent in the New Testament, suggesting that peace follows from God's grace.
from Him who is and was and is to come: God controlled the past, will control the future, and has complete authority and power over every present crisis (see also Revelation 1:8; 4:8; 11:17; 16:5).
the seven spirits: Some argue that the "seven spirits" are seven angels, but the phrase fits between references to God the Father (Revelation 1:4) and God the Son (1:5), making this passage a description of the Trinity (see Matthew 28:19; John 14:26; 15:26; 2 Corinthians 13:14; 1 Peter 1:2). The number seven acknowledges the holy spirit’s perfection (compare Zechariah 4:2, 6, 10).