John originally wrote Yer Blues as a dig against blues music, almost a sarcastic play on it. But lyrically its about his own personal insecruities. He wrote it during his time in India which explains all the deep meanings behind the stuff like ''mother was if the earth, father was of the sky.' His talking about being at one with everything..
He also named it Yer Blues to even out the seriousness behind the lyrical content a bit. Youll find he did that with most of his philosophical meaning songs such as 'Tommorow Never Knows' and 'I am the Walrus'..