Either way, whether you believe it was Samuel or it wasn't, the message is exactly the same. Samuel appeared from the dead in some shape or form, and delivered to Saul the message he had heard previously, but never taken seriously: the condemnation of God on his reign.
Some people are like this; indeed at some time, all people are like this. They just don't take God seriously. ‘You are doomed; your life is removed; you will perish; you will come under judgement.’ They tremble for a moment, and then say to themselves, ‘Not really. Surely, not really. There will be another opportunity. I can go on as I am.’ As Saul says, ‘Let me go to a medium; please get me Samuel.’ ‘Why?’ ‘Because I imagine somehow I can appeal to him at the last minute and make things right. And all the threats and all warnings and all the judgements: I can get past them.’ People think they can avoid some hard duty before the Lord by asking again in the hope of getting a different answer. Never imagine that! Even as a Christian, as a believer, under the smile and the kindness of God; when God says, ‘Don't do this, and don't do that’, take it seriously. Don't, like an unbeliever, like Saul, say to yourself, ‘I don’t think God will really disapprove of me if I just push along, keep doing this, keep doing that.’ What happened in the case of Saul was that, through the apparition of Samuel, the judgement of God was delivered to him, and he swoons out flat.