Boasting In God
Isaiah 25:9 (ESV) … “It will be said on that day, ‘Behold, this is our God; we have waited for him, that he might save us. This is the Lord; we have waited for him; let us be glad and rejoice in his salvation.’”
In this and the following verses the prophet proceeds to unfold more fully what he had just presented. When the salvation comes, then people will boast in their God. Then they will see that they did right in trusting the promises of God, and they will not be ashamed of their confidence. Their hopes will be fulfilled, and they can boast and rejoice therein.
In that day when God wipes away all tears, people will speak His praises. The verb is impersonal, and probably indicates the redeemed generally. Not only will Israelites praise Him, but all who have received His blessings. They will call attention to the God who has done such things for them and who is their own God. For Him, they say, they have waited, i.e., they have waited for Him to fulfill His promises in order that He might save them.33 They have believed that what He promised would be fulfilled in their own deliverance, and now they have seen that their hope was not in vain. Indeed, this God is none other than the covenant God of Israel, the Lord, in whom the people have placed their trust.
Therefore, the people encourage and exhort one another to rejoice and to exult in the salvation which they have received from Him. They may truly say that it is “His salvation,” for it comes from Him, and He is its author. The emphases in the verse are important. Note the suffix, His, and the word this. It is as though the nation had said, “This is the God of whom we have so often spoken. Look now, as we have trusted in Him, so He has brought to pass what He promised.”
 Young, E. (1969). The Book of Isaiah, Chapters 19–39 (Vol. 2, pp. 198–199). Grand Rapids, MI: Wm. B. Eerdmans Publishing Co.