Lyric discussion by dylan9236 

Cover art for Speak to Me lyrics by Pink Floyd

i reckon the line "its very hard to explain why you're mad, even if youre not mad" is the most important one in context to the whole album because it sounds as if he is trying to convince himself that he isnt mad (even tho he might in fact be perfectly sane) and is paranoid about his sanity and the issues in his life