Single

as it is used here in this verse, means,

Pure; simple; incorrupt; unbiased; having clear vision of the
divine truth.

Webster's 1828
American Dictionary
of the
English Language


The light of the body is the eye:
if therefore thine eye be single,
thy whole body shall be full of light.
But if thine eye be evil, thy whole body shall be full of darkness.
If therefore the light that is in thee
be darkness, how great is
that darkness!

Matthew 6:22-23