for goodness' sake; I beg of you
A pleading expression used when earnestly asking someone to do or not do something. Often carries a tone of desperation or strong entreaty. The phrase is a fixed expression and not broken down into separate words in modern usage.
For goodness' sake, please give me just one more chance.
I beg of you, stop talking about that.
The phrase originates from the Buddhist term 後生 (ごしょう, 'the afterlife'), combined with だから ('because'). Literally 'because of the afterlife', it evolved into an expression of earnest entreaty, as if staking one's future existence on the request.