In John's vision there was a multitude of people who worshiped the Creator. Tribute was given to Him as the source of our salvation.
It is no coincidence that in the first book of the Bible we were promised salvation from our sins (Genesis 3:15) and in the last we are given confirmation of that salvation (Revelation 7:10).
The word translated as salvation in this verse is the Greek word 'soteria'. It could also have been translated as deliverance from danger, slavery, imprisonment, destruction, sin, or the spiritual consequences of sin. It also implies victory over these things.
What am I saying? We were all prisoners of sin, destined for destruction as the consequences of our actions. But because of God's grace, the blood of His Son was shed for all of us. In Him we have victory.
We are highly privileged that the Creator came from heaven to die as the Lamb that takes our sin away. We should lift our voices as did the great multitude, in praise and adoration, because we have been delivered from sin.