It was working almost like a plan. It was possible to see Intention in it. (2.3.63)
Lee is very religious and sees a divine plan in things. One of the ironies of the battle is that he isn't aware that destiny is actually set against him: he's the one being built up for defeat. You could look at it another way, too: maybe Lee's faith in a divine plan blinds him to his own and his Army's weaknesses. If he didn't believe so strongly that fate was on his side, maybe he would have been more cautious, as Longstreet continually tells him to be.
His blood was rising. He had tried to be discreet, but it was all happening without him, without one decision; it was all in God's hands. And yet he could leave it alone himself no longer. Rodes and Early were attacking; Heth and Pender were waiting here in front of him. Lee's instinct sensed opportunity. Let us all go in together, as God has decreed a fight here. (2.3.63)
Lee senses that this battle is pre-ordained. But maybe, if he didn't feel that way, he might have avoided ordering Pickett's Charge, and the Confederacy might have somehow won the war?
With that word it was out of his hands. It had never really been in his hands at all. And yet his was the responsibility. (2.3.65)
Lee views himself as a servant. For him, God's in control, and he simply has a role to play in God's plan.
He believed in a Purpose as surely as he believed that the stars above him were really there. He thought himself too dull to read God's plan, a servant only. And yet sometimes there were glimpses. (3.6.13)
Lee believes he gets glimpses into the destiny of the nation—but in this case, he's actually blind to the workings of destiny. If he weren't, he wouldn't have ordered Pickett's Charge. Is it his fate to lose? Or does he just get himself into trouble by being too confident?
And so he took up arms willfully, knowingly, in perhaps the wrong cause against his own sacred oath and stood now upon alien ground he had once sworn to defend, sworn in honor, and he had arrived there really in the hands of God, without any choice at all; there had never been an alternative except to run away, and he could not do that. (3.6.25)
Lee couldn't run away, because he felt too devoted to his family and friends in Virginia. He couldn't put a principle—opposition to slavery—above the people he grew up with. But why couldn't he have refused to fight? Could he have taken his family and run away to Europe? Do you think Lee might just be making an excuse? Or not?
It was all set and fated like the coming of the bloody heat, the damned rising of the damned sun, and nothing to do, no way to prevent it, my weary old man, God help us, what are you doing? (4.2.69)
Longstreet can't understand Lee's actions. Lee feels that the course is set: in his mind, he's following a predestined pattern. But Longstreet wants to alter fate: he wants to swing the army around and cut the Union forces off from Lincoln in D.C.
Cannot leave because I disagree, because, as he says, it's all in the hands of God. And maybe God really wants it this way. But they will mostly all die. We will lose it here. (4.2.142)
Longstreet is in a tough position: he senses the way things are going, but he remains powerless to change anything—he can't convince Lee to alter his course. That's his tragedy—to be right but not be able to do anything about it.
He opened his eyes, looked a question at Heaven, felt himself in the grip of these great forces, powerless, sliding down the long afternoon toward the end, as if it was all arranged somewhere, nothing he could have done to avoid it, not he or any Virginian. (4.4.9)
Lee finally senses his true lack of control: he found it impossible to avoid ordering the charge, and it totally failed. He feels like there never was any other option, and the divine plan went against him. Was there any alternative? What about Longstreet's plan? Why didn't Lee listen to him? Was it fate? Or Lee's free will?