1) The effect of spiritual blindness is sin:

a) Isaiah 29:10 "For the lord hath poured out upon you the spirit of deep sleep, and hath closed your eyes."
b) Matthew 6:23 "But if thy eye be evil, thy whole body shall be full of darkness."
c) John 3:19-20 "And this is the condemnation, that light is come into the world, and men, loved darkness rather than light, because their deeds were evil. For every one that doeth evil hateth the light, neither cometh to the light, lest his deeds should be reproved."

a) II Corinthians 4: 3-4 "But if our gospel be hid, it is hid to them that are lost: In whom the god of this world hath blinded the minds of them which believe not..."

a) Ephesians 4:18 "Having the understanding darkened being alienated from the life of God through ignorance that is in them, because of the blindness of their heart."