He isn't. The Friar tells the whole story to the Prince after R&J are found dead and then says, "If aught in this miscarried by my fault, let my old life be sacrificed." In other words, he was inviting the Prince to find him guilty of anything leading up to the tragedy, including secretly marrying them and giving Juliet the potion. The Prince responds evasively, "We still have known thee for a holy man." Which means, probably, that if the Friar is at fault, he is completely forgiven and not found guilty at all, because he is a "holy man".
Friar Lawrence was guilty of marrying Romeo and Juliet in secret, giving Juliet the potion to fake her death, and not communicating his plans effectively to Romeo, which ultimately led to the deaths of Romeo and Juliet.
In my opinion, Friar Lawrence is guilty for Romeo and Juliet's death. I think he is guilty because he married Romeo and Juliet. He gave Juliet the potion, and because he didn't get the message to Romeo, I think that he should have met up with Romeo on the outside of Capulet's tomb. Or maybe he could of gone to Mantua and met with Romeo face to face.
Friar Lawrence prepares the potion for Juliet in William Shakespeare's play "Romeo and Juliet."
Juliet worries that Friar Lawrence's sleeping potion is actually a poison.
A potion cooked up by Friar Lawrence.
Juliet never doubts that Romeo will come for her. She does have doubt about Friar Lawrence and that he might have changed the potion to poison.
Juliet says, "Romeo, I come! This do I drink to thee!" and she drinks Friar Lawrence's potion.
The plant root used in Friar Lawrence's sleeping potion is called mandrake root. It is a poisonous plant with a long history in folklore and mythology and is often associated with magical and mystical properties. In Shakespeare's play "Romeo and Juliet," Friar Lawrence uses mandrake root in the potion that puts Juliet into a deep sleep to feign her death.
She will become near-death, her veins will go cold, her heart will stop for 2 days.
Romeo and Paris both thought Juliet was dead when she was only asleep from the potion Friar Lawrence gave her.
Friar Lawrence, in Act 5 Scene 2.
She asks Friar Lawrence for help. He was the one to give her the potion that will put her to sleep for 42 hours.