"So will fall
He and his faithless progeny. Whose fault?
Whose but his own? Ingrate! He had of Me
All he could have; I made him just and right,
Sufficient to have stood, though free to fall" (3.95-9).
God makes it clear that Adam will fall through his own "fault." Even though this sounds like predestination, it's actually foreknowledge. God sees all events – past, present, and future – as simultaneous or present, including Adam's fall, which hasn't happened yet (in the poem). Just because God knows it will happen though doesn't mean he makes it happen; He knows how Adam himself will make it happen.
Quote 2
"advise him of his happy state—
Happiness in his power left free to will,
Left to his own free will, his will though free
Yet mutable" (5.234-7).
The repetition of "free will" in this passage points to its importance and centrality in the poem, but the tortured syntax makes the issue more complicated than a simple matter of emphasis. Adam can control his own happiness ("left free to will"), but free will can turn into something else if he's not careful. What exactly? We're not sure.
Quote 3
"No Decree of mine
Concurring to necessitate his Fall,
Or touch with lightest moment of impulse
His free Will, to her own inclining left
In even scale" (10.43-7)
God reiterates a point he's made throughout the poem. Not even the "lightest…impulse" from God has affected Adam and Eve's behavior. Note the importance God places on words associated with the fate versus free will debate: "decree," "necessitate," "impulse," and "inclining."