The easiest example is the statement near the start of Book II:
Me though just right, and the fixed laws of Heaven,
Did first create your leader--next, free choice
With what besides in council or in fight
Hath been achieved of merit--yet this loss,
Satan indicates this war is free choice.
"for so I formd them free, and free they must remain"
This phrase reflects the free nature of man and the will of God to keep him that way. The entire third stanza of book 2 reflects the idea that, though God knew what would happen in the end, man could not truly love without free will and predestination had no influence on them. Instead of removing from man free-will in order to keep him from being disobedient, he decides that he will send His Son as a sacrifice so that they might choose to believe in Him and be saved. Those who choose otherwise will suffer the consequences of eternity in Hell.