"Don't mistake it.  There are plenty of times when Satan who always is accusing the brethren, is given permission [bad word] after believers for God's own purposes.  And what his purpose is, is indicated to us in verse 32, this is one of the greatest statements in the Bible.  Verse 32, "But I have prayed for you that your faith may not fail." And when Jesus prays, His prayer is answered.  He always prays according to the will of God, just like the Holy Spirit, Romans 8:26.  He always prays in the will of God.  "I have prayed for you."  This is the high priest interceding for us at the right hand of God.  I have prayed for you that your faith fail not.  Satan wants to prove that he can destroy saving faith.  That's the old effort.  That's the age-old effort.  Satan says, "Let me at him and I'll destroy their [bad word] in You, I'll destroy their faith in You." 

And you want to know something?  If it was left up to us, he would.  I've told you this before.  If I could lose my salvation, I would lose it.  If it were possible, it would happen.  If I had to save myself, I couldn't save myself.  If I had to keep myself saved, I couldn't keep myself saved.  My faith cannot fail not because of me but because of the one who secures my faith by His own intercession.  And when Satan goes, according to Romans 8, before God and lays an accusation before God against us, it does not stand.  Who can lay any charge to God's elect?  It is Christ that justified.  Christ has already paid in full the penalty for our sin, declared us just, granted us righteousness and therefore no condemnation can stand against us.  And Paul goes on to say, "Then what's going to separate us from the love of Christ?" And the answer is, "Absolutely nothing...nothing."  No accusation stands against us.  Our great High Priest is for us and if God is for us, who can successfully be against us?  I love that.  "I have prayed for you." That's personal."
- John MacArthur, Table Talk on Trouble and Triumph, Part 2

 [bad word] /www.gty.org/Resources/Sermons/42-271 )