In Paradise Lost does Milton ever show real symapathy for Satan? Do we get any autobiographical glimpses in it?How do we interpret Satan's soliloquy?
It is popularly known that Milton was a Puritanic Protestant and he never sympathized with a religious outcast or an atheist.
Be not deceived! Our enemy the devil goes about like a prowling lion, seeking whom he may destroy!
The reason you are confused is because Satan is the father of lies. Milton purposefully portrays Satan in a sympathetic way at the beginning of Paradise Lost so that his readers will also sympathize with him. He is hoping to show readers that Satan is crafty - looks good on the outside, but is evil on the inside. The Bible also warns that Satan is not always a "prowling lion" and that he was once the angel of light, so sometimes his evil looks mighty tempting. That is why he was able to trick Adam and Eve into eating the fruit - he lied to them. He said, "You will not die! God just doesn't want you to be like him!" So they ate. But this was not true.
In the beginning of this epic, Satan gives great, leadership intense speeches. He rallies all of the devils to his side. His speeches in the beginning all present him as almost heroic. However, as the epic unfolds, we gradually witness his demise. He decides to forsake trying to get back into heaven and live on earth after all, and this is where Milton finally unveils him as the true deceiver that he is. All along, Satan's goal is evil - trying to drag as many people down with him as possible. So, while readers may identify with him in the beginning (because he is a lot like fallen man!), in the end, his sin of pride is exposed and we see that Satan does not have any good intentions towards mankind.
People that think Milton sympathized with Satan do not understand his religious beliefs, that is why there is some confusion over this. Satan only seems heroic in the beginning because we recognize ourselves in him. Pride goes before the fall!