Jamieson, Fausset and Brown on 2 Corinthians 1:18

18. He adds this lest they might think his DOCTRINE was changeable like his purposes (the change in which he admitted in 2Co 1:17, while denying that it was due to "lightness," and at the same time implying that not to have changed, where there was good reason, would have been to imitate the fleshly-minded who at all costs obstinately hold to their purpose).

true--Greek, "faithful" (1Co 1:9).

our word--the doctrine we preach.

was not--The oldest manuscripts read "is not."

yea and nay--that is, inconsistent with itself.