How does Decius persuade Caesar to go to the Senate House?

Decius knows that Julius Caesar really wants to go to the Senate House because he is expecting the senators to make him a king. The only obstacle to getting Caesar to go is his wife Calpurnia. She has had one particularly bad dream and feels sure that her husband will be going to his death if he leaves their home. 

Decius first discounts Calpurnia's dream by reinterpreting it.

This dream is all amiss interpreted;
It was a vision fair and fortunate.
Your statue spouting blood in many pipes,
In which so many smiling Romans bathed,
Signifies that from you great Rome shall suck
Reviving blood, and that great men shall press
For tinctures, stains, relics, and cognizance.
This by Calpurnia's dream is signified.   (II.2)

Caesar quickly approves of Decius' interpretation of Calpurnia's dream. This sets Caesar up, so to speak, for what Decius has to say next.

                ...the Senate have concluded
To give this day a crown to mighty Caesar.
If you shall send them word you will not come,
Their minds may change. Besides, it were a mock
Apt to be render'd, for some one to say
“Break up the Senate till another time,
When Caesar's wife shall meet with better dreams.”
If Caesar hide himself, shall they not whisper
“Lo, Caesar is afraid”?               (II.2)

So, according to the wily Decius, if Caesar goes to the Senate House he will receive the crown for which he has been scheming for a long while. It will be the culmination of Caesar's dreams of glory. But, on the other hand, if he stays at home today, the senators may change their minds. They may feel resentful because they have been slighted. They may think that Caesar doesn't really want the crown. After all, he appeared to be refusing it three times when Mark Antony offered it, or some facsimile of a crown, at the Lupercal games. Furthermore, the senators may lose their high opinion of Caesar if they suspect he is afraid to come because of his wife's bad dreams. 

Caesar prides himself on his courage. He can't allow himself to be kept at home by his wife's fears. He tells her:

How foolish do your fears seem now, Calpurnia!
I am ashamed I did yield to them.
Bring me my robe, for I will go.       (II.2)

Act II, Scene 2 might end with the line "Bring me my robe, for I will go," except that Shakespeare evidently wanted to show the servant going to fetch the robe and coming back with it to help his master put it on. The robe will be important in Act III, Scene 2 when Antony will show a duplicate robe to the plebeians which is shredded and bloodstained. Among other things, the duplicate robe will remind the theater audience that Calpurnia was right in trying to keep her husband at home and Caesar wrong to listen to Decius.