Listen.Steve Harris the founder and bassist of iron maiden, one night before he wrote that song he saw some scaring movies about satan etc.So when he went to sleep he had a vision-dream.In that dream he saw satan and some other things like that and he was really scared.The next day a friend of him had an accident and I Think that friend was in the directoring team of the album or something like that.Also some other incidents happened with the numbers 666.That's why Steve Harris wrote Hallowed be thy name and The number of the beast.He was inspired by some things that happened .In addition they told that in the studio there was a special atmosphere.Like something was with them.Anyway some believed that iron maiden were satan worshipers but that's fade n gay.I've read all these things in wikipedia one year ago so I might be wrong in some facts.I don't remember well.If you want take a look there.
I'm actually sure about Stairway to heaven and Iron Maiden's Number of the beast.Regarding the second one I know the whole story about how it was written and noone can doubt it.
I have variable opinions about this.
First of all, a friend of mine made a vocal cover of stairway to heaven, we reversed it and it didn't sound like that.The lines with the satanic meaning.
But I think they wanna express something via this.