Adam Clarke on Isaiah 25:9

It shall be said "Shall they say" - So the Septuagint and Vulgate, in the plural number. They read ואמרו veameru, the Syriac reads ואמרת veamarta, thou shalt say. They shall say, i.e., the Jews and the Gentiles - Lo, this [Jesus Christ] is our God: we have waited for him, according to the predictions of the prophets. We have expected him, and we have not been disappointed; therefore will we be glad, and rejoice in his salvation.