The answer to the #riddle -
I am a treasure widely unknown.
I cast a shadow not of my own.
I am a preacher, yet I do not talk.
I am a journey that two can walk.
The answer is "a godly marriage".
I am a treasure widely unknown
(a godly marriage is of immense value, but, sadly, rarely seen)
I cast a shadow not of my own
(a godly marriage reflects the heavenly marriage between Christ and His bride and marriage on earth foreshadows this deeper truth)
I am a preacher, yet I do not speak
(a godly marriage is a witness to unbelievers, portraying Christ's love for his church)
I am a journey that two can walk
(marriage is a journey that a husband and wife walk together)
Thanks to @erdenpilger for the riddle.