World Wide Study Bible
a Bible passage
41 Isaiah said this because he saw his glory and spoke about him.
41. These things spoke Jesus. Lest readers should think that this prediction was inappropriately quoted, John expressly states, that the prophet was not sent as a teacher to a single age, but, on the contrary, that the glory of Christ was exhibited to him, that he might be a witness of those things which should take place under his reign. Now the Evangelist takes for granted, that Isaiah saw the glory of Christ; and hence he infers, that Isaiah accommodates his instruction to the future state of Christ’s kingdom.