Lamb to the slaughter

Meaning

In an unconcerned manner - unaware of the impending catastrophe.

Origin

From the Bible (King James Version),

Jeremiah 11:19:

But I was like a gentle lamb led to the slaughter; And I did not know that they had devised plots against me, {saying,} "Let us destroy the tree with its fruit, And let us cut him off from the land of the living, That his name be remembered no more."

and Isaiah 53:7:

He was oppressed, and he was afflicted, yet he opened not his mouth: he is brought as a lamb to the slaughter, and as a sheep before her shearers is dumb, so he openeth not his mouth.

In addition to lambs, other verses in the Bible has other animals going 'to the slaughter', i.e. oxen, bullocks and sheep. The allusion to the especial helplessness of lambs was made use of in the 1991 film The Silence of The Lambs.

Geoffery Chaucer laid the groundwork for the phrase in the Man of Law's Tale, 1386:

For as a lamb is brought to slaughter, so
She stands, this innocent, before the king.