In Act II, Scene 8 of The Merchant of Venice, why does Shakespeare choose Solanio and Salarino to tell us information that they witnessed?

Salarino and Salanio are given the task of presenting information to the audience in Act II, Scene 8, because they can give candid reports about other characters and because they serve the important function of establishing foreshadowing. It is not until after the Romantic period that unreliable characters are introduced in literature, so it is a forgone conclusion that, while friendships and roles may bias the delivery of information, the information is trustworthy.

Renaissance drama is built upon Greek drama in which the Chorus is routinely used to tell the audience important information about characters, character motives, actions, and events that aren't acted out by the principles on stage. Shakespeare kept the function of using non-principle characters to convey needed additional information but he substituted the Chorus with three other kinds of characters. The first is the Fool, an urban character who is a favorite at court and jests with and about the primary characters letting us know more about the deeper thoughts, traits, and motives of the principles.

The second is the Clown who is similar to the Fool except that the Clown is country bred and uneducated and leads the audience to a deeper understanding of the primary characters by blundering along without knowing what he is really doing. The third kind is that of which Salanio and Salarino are representative: minor characters who fill the place left by the elimination of the Chorus and who reveal important information to the audience about the primary characters and events because they have privileged positions and know things that others don't.

In this capacity, Salanio and Salarino tell about Shylock's reaction to the devastation of his daughter's betrayal, elopement, and early access to her inheritance (some of which is Shylock's present working capital) and they tell about Lorenzo's and Jessica's flight from Venice and they tell about Antonio's private conversation with, feelings for, and instructions to Bassanio. They also tell that a ship has been lost in the English channel and that they suspect it might Antonio's, which foreshadows his loss and his upcoming trouble with Shylock: "Let good Antonio look he keep his day [on which to repay his loan], / Or he shall pay for this [through Shylock's demands]."