A.T. Robertson Commentary John 20:29

"Jesus saith unto him, Because thou hast seen me, thou hast believed: blessed [are] they that have not seen, and [yet] have believed." — John 20:29 (ASV)

Thou hast believed (πεπιστευκας). Perfect active indicative. Probably interrogative, but "it was sight, not touch that convinced Thomas" (Bernard).

And yet (κα). Clear use of κα in the adversative sense. Thomas made a noble confession, but he missed the highest form of faith without the evidence of the senses. Peter (1 Peter 1:8) uses language that seems like a reminiscence of the words of Jesus to Thomas which Peter heard.