Explain the signigificance of the following quote.

Line numbers don't always match up but I'm pretty sure you mean this.

Macbeth is trying to wear his big boy pants. The tables have been turned and now L. Macbeth is out of the murdering people loop. This of course means Banquo!

"Be innocent of the knowledge, dearest chuck, till thou applaud the deed….."

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The shard-borne beetle with his drowsy hums

Hath rung night’s yawning peal, there shall be done

A deed of dreadful note.

It is Banquo and his son Fleance's death sentence. Macbeth is proclaiming they'll be dead before nightfall.