The lines beginning with 'For you are beautiful' have the same words in all three verses of this generally likeable song. The wore 'you' in them refers to the islands that the singer is leaving and bidding farewell to. In the first two verses the song manages a fitting logical connection (as implied by the word 'for') with the lines leading up to 'For you are beautiful....'. But here in the third verse, it just couldn't manage a thrid similar logical connection. The beauty of the islands he's leaving just can't sensibly be the reason for his anticipated watching of the English mist rolling through the dell. So the word 'For', so fiting in previous verses, is simply impertinent this time.