Luke concluded his quote of Isaiah with the saying that all flesh will see (καὶ ὄψεται πᾶσα σὰρξ) the salvation of God (τὸ σωτήριον τοῦ Θεοῦ). However, that is not from Isaiah who said that the glory of Yahweh would be revealed. All the people would see it together. I suppose that the intent is pretty much the same. Deutero-Isaiah was talking about Yahweh saving his people from Babylon. Thus, this might be considered a unique saying of Luke.
Once again, this is reminiscent of the vision in chapter 1. The cherubim in the Temple were surrounding the Holy of Holies on the south side of the Temple. The man in linen cloth with the writing case at his side went into the sanctuary as a cloud filled the inner court. Then the glory of Yahweh rose up from the cherubim and moved to the threshold of the Temple as in the last chapter. This glory of Yahweh was the real presence of God. The whole Temple was filled with a cloud, while the court was full of the brightness and glory of Yahweh. The sound of the wings of the cherubim could be heard as far away as the outer court, as in chapter 1. They sounded like the voice of God Almighty when he spoke.