29 Jesus saith unto him, Thomas, because thou hast seen me, thou hast believed: blessed are they that have not seen, and yet have believed.
Jesus is talking to Thomas about seeing Him in the physical realm, not spiritual, but those that don't see in the physical and believe are blessed. You left out several important verses for context.
[Jhn 20:27-29 KJV]
27 Then saith he to Thomas, Reach hither thy finger, and behold my hands; and reach hither thy hand, and thrust [it] into my side: and be not faithless, but believing.
28 And Thomas answered and said unto him, My Lord and my God.
29 Jesus saith unto him, Thomas, because thou hast seen me, thou hast believed: blessed [are] they that have not seen, and [yet] have believed.