Does Satan know who the Redeemed are? Or is he blind to who the truly Redeemed are?
Yes, he and his spirits recognize the Holy Spirit in those who are Redeemed, and he accuses them day and night before God. Those Jews who accused Paul (and Jesus) in Acts were doing the will of their father, Satan.
Does Satan understand the Redeemed man's eternal security?
He
knows the decree of man's salvation as he heard God's curse upon himself and God's blessing upon the seed of the woman, in Genesis 3. However, he doesn't seem to
understand exactly how sovereign God is over all things. Namely....
If he does, what is the purpose of his tormenting of the saints of God if he realizes he can't have them? Is it a venting of his wrath, knowing his time is short and trying to bask in as much glory for himself as possible?
Satan and his angels love to see us suffer. They study us and know our weaknesses and try every attempt to thwart our peace with God. They know and hate how content we are in the fellowship with the Lord, basking in His grace and glory (wrote that before reading your last question!), and they torment us to see how we are when we sin against God.
Satan
wanted to, desired to, lusted after seeing Adam and Eve transgress the law and the following calamity. Satan is evil, chaotic, irrational, and assumes as his own those who do not belong to God, for Jesus said,
You are of your father the devil, and the desires of your father you want to do.
Satan may be venting his wrath, getting in every last evil deed that he can through the sons of men until his judgment and damnation; making all who do not love God worship him. But as far as the purpose of it all, is not so much to perform as many evil deeds as he is able in quantity, but to see the pain and suffering of those who love God. That's his goal. He's the slanderer, the accuser, accusing us before God day and night, as he did with Job. And God used Job as a demonstration to Satan and the heavenly court of just how sovereign He is over Satan's near-sighted lusts and man's near-sighted questions.
More so, God used the life of Jesus, the cross, the slaughter of the Son of God to demonstrate His righteousness in the most profound, convincing, and direct way possible. Much of what goes on here is a sign to the angels, good and bad. And we will, indeed, judge the (fallen) angels.
Does he believe he can make Christ's atonement futile?
When Satan saw the crucifixion, he knew his head was about to be crushed. And he now knows he is truly defeated because Jesus was raised from the grave, conquering sin and trampling death.
He knows he can do no such thing, although he and his angels likes to teach Arminians that he can (ie conditional salvation). And the Arminian's doubts of God's effectiveness in saving someone, and the resulting shame they bring when one of them "falls from grace," is exactly the way he wants to see Christians feel. "I've done too much wrong, I've backslidden too far, I can walk out of God's hand. And what I've done wrong he can't forgive, He can't bring me back, I'm unworthy of Christ's blood."
These thoughts do, in a way, make Christ's atonement "futile,"
but only in their minds, for a born-again child of God will always be brought back and persevere, all that Christ has atoned for will always be atoned for; those who superficially apply the atonement to themselves and reject God's forgiveness when they realize they can't be sinless or perfect in this life were never purchased.
Or should I not even bother with questions like those?
Bother with these questions, and all things -- we worship God in spirit and truth, in His Spirit of power, love, and a sound mind. Not to mention we are commanded to love God with all of our mind, too!!
But there are things that are too wonderful for us to know, and we may veer into seeking knowledge for the sake of knowledge, not for the sake of loving and glorifying God, but God will surely rebuke us if that happens, just as he did Job, and we with Job will say,
I know that You can do everything,
And that no purpose of Yours can be withheld from You.
You asked, 'Who is this who hides counsel without knowledge?'
Therefore I have uttered what I did not understand,
Things too wonderful for me, which I did not know.
