Luke let the Scriptures speak for himself. Sanders reports:
And here is a major observation about Luke's knowledge of his scripture: In no case of Luke's reading and understanding of scripture does one have to go to a Pharisaic-rabbinic type Jewish interpretation of an Old Testament passage to see how Luke moved through the ancient text to his modern message. Quite often one must rummage around in the targummim, midrashim, and Jewish commentaries before one finds the key to how an Old Testament passage functioned for Matthew. He was sometimes dependent on a particular interpretation or understanding of a passage of scripture: indeed, it would have been that which he had in mind even as he read or cited a text. Not so Luke. (Sanders, “Isaiah in Luke, 146.)
It appears that Luke depended very little on others’ interpretations of Isaiah, choosing instead to let the straight reading of the Scriptures speak for themselves, though he certainly made interpretive decisions. This is a sound principle for modern day narrators of the gospel. The Scriptures are powerful and effective (Heb. 4:12). While interpretation is necessary, one ought not lean more heavily on the interpretations of men than on a simple, straight reading and the power of the Holy Spirit.