What did our earlier brothers and sisters in the family of Abraham believe in this vital matter [of one way of salvation]?
First, not only that salvation arises from God but that He is Himself ‘salvation’ (v.2); it is one way of defining what He is. When we stand before Him we stand before salvation. This is our supreme ground of assurance: God, who in other circumstances would be our judge, unapproachable in holiness, is Himself our salvation.
Secondly, we need salvation because of the wrath of God against sin and sinners (Rom. 1:18) — not because sin damages or mars us (though it does) but because it enrages and alienates Him.
But, thirdly, Isaiah saw this exasperated anger fade away and be replaced by comfort (v.2). He does not say here how that seemingly impossible change has come about, because he has already told what had happened. In 6:6-7 he saw the Seraph bring to him the fire from the altar; evidence that the fiery wrath of God had burnt itself out on the body of a substitutionary sacrifice.
In the fourth place, salvation is, on our side, by faith: when we ‘trust’, all fear and apprehension disappear.
Fifthly, the salvation into which we enter once for all by faith is constantly available, never exhausted: we enjoy free access to the fountains of fresh supply.
And finally, the same wondrous God who is ‘salvation’ is also our strength for the road and the joy which transforms.
Salvation from God; salvation by faith; salvation in endless freshness; salvation ministering strength and delight!
— Alec Motyer, Isaiah by the Day, 75 (emphasis added).