While both Jupiter and Neptune symbolize faith and spirit among other things, there’s a difference.
Jupiter is more about going it the establishment route: church dogma, preaching, order.
Neptune on the other hand is free-wheeling, love-all, no boundaries kind of spirituality.
What makes it even more so are the signs: Jupiter is in Virgo, and Neptune in its own sign, Pisces, where it’s especially strong.
Jupiter in Virgo tends to bring out the preacher, the stickler to the rules, and sometimes critical kind of faith and spirituality.
Neptune in Pisces is dreamiest of dreamer, and out-there spiritual person who dislikes religious rules intensely while believing spirit is everywhere.
Both really reach out for the same, just going different routes, I believe.