Jamieson, Fausset and Brown on John 3:11-13

11-13. We speak that we know, and ... have seen--that is, by absolute knowledge and immediate vision of God, which "the only-begotten Son in the bosom of the Father" claims as exclusively His own (Joh 1:18). The "we" and "our" are here used, though Himself only is intended, in emphatic contrast, probably, with the opening words of Nicodemus, "Rabbi, we know.", &c.

ye receive not, &c.--referring to the class to which Nicodemus belonged, but from which he was beginning to be separated in spirit.