It is to accept
I cannot accept the first four lines without a clear understanding that they apply only with regard to the Tao: not to what anyone says about the Tao or to anyone who claims to speak for the Tao. Even the wisest sage must be rebuffed if he or she asks for blind faith (that is what is being described in the first four lines). I think that blind faith is almost always bad faith and any human who asks for it is arrogant, presumptions, dangerous and unenlightened, no matter what her or his credentials may seem to be.
The poem is rescued by its last three lines: Faith is accepting silence silently. Maybe not a total definition, but a good start.