In The Merchant of Venice, explain Shylock’s repetition of the sentence, “Let him look to his bond” (III.i. 43).

What is important to focus on in this scene is the way in
which Shylock has just suffered the loss of everything that is important to him in life:
his daughter, Jessica, has eloped with the Christian Lorenzo, and has also stolen all of
his wealth when she left. He is a man desolate and empty. Thus it is that the only thing
he has to cling on to in life is the "ancient grudge" that he has against Christians and
in particular, Antonio. The "merry bond" that he made with Antonio is now his only focus
and the way that he obsesses about it and single-mindedly looks toward the time when he
can gain his revenge for all of the tragedies he has suffered is underlined through the
repetition of the phrase you have indicated. Note what he says to Salerio and
Solanio:

A
bankrupt, a prodigal, who dare scarce show his head on the Rialto; a beggar, that was
used to come so smug upon the mart! let him look to his bond. He was wont to call me
usurer. Let him look to his bond. He was wont to lend money for a Christian courtesy.
Let him look to his
bond.

Note the way that
before each repetition of the phrase Shylock cites yet another grievance he has against
Antonio. The repeptition of the phrase "Let him look to his bond" seems to underscore
the inevitability of the judgement that Shylock anticipates exacting against his enemy
and his keen anticipation in doing so.