Milton's implicit challenges to epic convention, already apparent in his representation of Satan as a parody of a (pagan) epic hero, are continued in the Invocation to Book IX. See its redefinition of what has been considered (in previous epics and chivalric romances) to constitute the "heroic"--Miltonís emphasis on patient fortitude, suffering, "standing" as opposed to aggressive aspiration and competitive violence.
See IV.419ff for Adam's emphasis on abstention from the fruit of the Tree of Knowledge as a "sign" of obedience, a purely symbolic act.
Compare the passage to what Milton writes in his theological treatise On Christian Doctrine:
It was necessary that something should be forbidden or commanded as a test of fidelity, and that an act in its own nature indifferent [arbitrary, immaterial], in order that man's obedience might be therefore tested . . . It was called the tree of knowledge of good and evil from the event [the consequences of eating]; for since [i.e., ever since] Adam tasted it, we not only know evil, but we know good only by means of evil.
Milton argues that the tree is not the Tree of Knowledge because it represents or contains or marks a kind of knowledge purposely withheld from Adam and Eve. But to eat of the tree is to disobey God and thus to acquire the knowledge of what it is to transgress, to apprehend evil for the first time, and to know absolute good thereafter only as something that one has lost.
For Adam and Eve to be "heroic" in the terms of Milton's Christian epic, all they must do is STAND against temptation; stand firm in choosing NOT TO ACT, in choosing to abstain from the one thing prohibited them in Paradise.
Milton's elaboration of Genesis gives us two quite separate and rather differently motivated "falls" in Book IX. His complication of the fall of MAN is an abiding tension in this poem:
"Do not believe" (IX.684), "look on me" (IX.686), Satan says. Satan will achieve his ends if...
Note the slipperiness of satanic logic:
His response to Eve's invitation to eat: the agonized inner soliloquy (894ff) versus the public performance (917ff) of acquiescence. Consider particularly the rationalizations of the latter; contrast them with Adam's recognition of the implications of Eve's act--and his decision, nevertheless, to act in solidarity with her lest he lose her: he prizes his bond with Eve over his obedience to God.
Is it possible for the fallen reader not to identify with Adams action? The temptation (from a Miltonic perspective) to read his self-sacrifice as "heroic" ...
Milton's representation of the consequences of the second fall: