He wants to save her life, and perhaps he is moved by the intensity of her love. To be specific, she says she'll kill herself rather than marry Paris. Rather than let her do that, he will help her pretend to die, so that she can escape her family's will and marry Romeo.
The potion will put her into a (death-like) sleep from which she can then awaken; that's what the other line means.
Why did Friar Laurence persuade Juliet to drink the potion?
What does the literary term mean "And then awake as from a pleasant sleep"?
Friar Lawrence persuaded Juliet to drink the potion because he didn't want Juliet to kill herself because she threatened to kill herself if she had to marry Paris.
Friar Lawrence also had a realization that both the Montagues and Capulets could finally get along because they've had a long, hateful relationship.
There are a number of reasons: 1) Juliet threatened to kill herself if he offered no solution, and he didn't want that. 2) He wanted to end the feud between the two families, and if he saved their marriage it'd be easier. 3) He wants Romeo and Juliet to be happy.
maybe cause he knew that she wanted to be with romeo badly