C.K. Barrett on 1 Corinthians 8:6

Jesus Christ is not described as God, and the fact that Lord (κυριος) serves very frequently in the Greek Old Testament as an equivalent of the Hebrew name of God (YHWH) loses some force from the fact that it was also used in a variety of other senses, for example, it might be no more than ‘Sir’, used as a polite form of address. It is always important to note the context in which Lord is used. Here it evidently stands in close relation, but is not identical, with God. Christ, in Paul’s usage, is seldom more than a second personal name, but its use means that Paul accepted the belief that Jesus was the Messiah whose coming Judaism awaited; in him the promises of the Old Testament were fulfilled (cf. 2 Cor. i.20). To the Hellenistic world Lord was a more meaningful way of expressing the divine kingship of Jesus than messianic terminology could provide. (C.K. Barrett, The First Epistle to the Corinthians [2d ed.; Black’s New Testament Commentaries; London: A&C Black, 1971], 193)