Albert Barnes Commentary Isaiah 25:9

"And it shall be said in that day, Lo, this is our God; we have waited for him, and he will save us: this is Jehovah; we have waited for him, we will be glad and rejoice in his salvation." — Isaiah 25:9 (ASV)

And it will be said in that day – By the people of God. This will be the language of exultation and joy that they will use.

Behold, this is our God – This is the language of those who now see and hail their Deliverer. It implies that such deliverance, and such mercy could be bestowed only by God, and that the fact that such mercies had been bestowed was proof that he was their God.

We have waited for him – Amidst many trials, persecutions, and calamities, we have looked for the coming of our God to deliver us, and we will rejoice in the salvation that he brings.

This is the Lord – This is Yahweh. It is Yahweh that has brought this deliverance. None but he could do it. The plan of redeeming mercy comes from him, and to him are to be traced all the benefits that it confers on man.