David Thibodeau — a survivor of the infamous 1993 Branch Davidians siege in Waco, Texas — is giving Justin Bieber some sage advice on religion, as some of his former friends question his association with Churchome.

Justin’s inner circle’s been getting smaller, and we’re told part of the reason is former friends believe Churchome, the Christian church he attends, is a cult, and Thibodeau has a lot of experience in that area, having been a member of the Branch Davidians — the David Koresh-led cult that had a weeks-long standoff with the feds before their Waco compound burned to the ground, killing more than 80 members.

Thibodeau told us he sees a lot of good and some bad in the case of Justin and Churchome. He says one major positive is the org is nowhere near as hardcore as the Branch Davidians were.

For starters, Churchome is not a 24/7 operation like the Davidians … in fact, the church only meets once a month — which David says gives Justin time and freedom to research other religions, if he chooses to do so.

Thibodeau warns JB, “Don’t go against that pit in his stomach that says something is right or wrong?” He also cautions Justin to be wary of Churchome’s leadership if they only have him read “the scripture” with no outside influences.

David also mentions Bieber should be thankful he’s older now because younger, less sophisticated people are more susceptible to being lured into a religious group or cult, just like what happened to him with the Davidians.

What’s more, Thibodeau says if Justin’s friends attack the singer’s faith or church — it would only serve to strengthen Justin’s bond with the church. He offers a better approach for those around him who disagree with Churchome.

In our documentary, “TMZ Investigates: What Happened to Justin Bieber?” — available now on YouTube — we told you about Justin’s ex-pal Ryan Good‘s falling out with the singer.

Ryan was a Churchome member, but sources told us he left because he thought it was a cult … something its pastor, Judah Smith, has adamantly denied.

A couple of interesting facts … Thibodeau was just a long-haired hippy when he was led out of the Koresh compound in handcuffs in 1993.