Question about Christianity...?

Well, I am a Christian... Or so I think... Hints, my question. I got "saved" in kindergarten, and my interest in Christ grew rapidly until high school, at which it decreased. I find myself with kids using profanity, and doing nothing about it, whereas just 2 years ago, I was desperatley trying to convert two of my friends for using the Lord's name in vain. I want to "renew" my salvation. Now, I know you are supposed to believe in Christ. Says John 3:16... But, SATAN believes in God but why isn't he "not perishing and living eternal life"? Clearly, there must be more... Please help! And if you are going to write a comment against Christianity... Well, don't.