Matthew 21:22
And
all things, whatsoever ye shall
ask in prayer, believing, ye shall
receive.
James 4:3
Ye
ask, and
receive not, because ye
ask amiss, that ye may consume it upon your lusts.
Anything you ask for in God's will, you will get. And certainly to ask for a believer to not lose faith, or the strength to withstand the trails they face is a prayer within God's will.
Praying for wisdom will always be answered with a "yes".
Now why did Jesus pray for Peter? What is the purpose of prayer? Prayer changes us, it doesn't change God because His will is already determinate. We pray for His will be done and help to know and accept that will.
I think Jesus prayed for Peter in this instance because Peter was clueless that he was in need of prayer.
I have a 17 year old son who's quite ill. He could die of his epilepsy and if that's what it comes to; I pray that God give him comfort to go in peace, because at this point, I'm not concerned for his redemption. He's been "woke" and he believes.
Not when you take the entirety of Scripture in context it doesn't.
A lot of people quote this verse outside of the context it's written in. Peter is addressing believers.
2 Peter 3:9
The Lord is not slack concerning his promise, as some men count slackness; but
is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance.
And God does know that everyone won't repent. Why won't they repent. Because repentance unto salvation is an outcropping of the work of the Spirit.
REPENTANCE:
Romans 2:4
Or despisest thou the riches of his goodness and forbearance and longsuffering;
not knowing that the goodness of God leadeth thee to repentance?
Acts 5:31
Him hath God exalted with his right hand
to be a Prince and a Saviour,
for to give repentance to Israel, and forgiveness of sins.
Jeremiah 31:17-19
And there is hope in thine end, saith the LORD, that thy children shall come again to their own border.
I have surely heard Ephraim bemoaning himself
thus; Thou hast chastised me, and I was chastised, as a bullock unaccustomed
to the yoke:
turn thou me, and I shall be turned; for thou art the LORD my God.
Surely after that I was turned, I repented; and after that I was instructed, I smote upon
my thigh: I was ashamed, yea, even confounded, because I did bear the reproach of my youth.