The meaning and origin of the expression: For ever and a day

For ever and a day

What's the origin of the phrase 'For ever and a day'?

Of course, for ever and a day is an dramatic construct with no literal meaning - for ever is for ever, we can't add days to it. This form of dramatic emphasis has been used many times, a recent example being The Beatles' song 'Eight Days a Week' and the widespread use of 110% effort.

Shakespeare coined 'for ever and a day' and used it in The Taming of the Shrew, 1596:

BIONDELLO: I cannot tell; expect they are busied about a counterfeit assurance: take you assurance of her, 'privilegio ad imprimendum solum:' to the church; take the priest, clerk, and some sufficient honest witnesses: If this be not that you look for, I have no more to say, But bid Bianca farewell for ever and a day.

He must have liked it as he used it again in As You Like It, 1600:

ROSALIND: Now tell me how long you would have her after you have possessed her.
ORLANDO: For ever and a day.