We need to hold in mind Petruchio's overall purpose and what he is trying to achieve to fully appreciate what he does in this hilarious act. He is engaged in trying to "tame" the "shrew" that he is about to marry, and will stop at no strategy in order to achieve this goal. This is why we see a marked shift in how he treats Katharina. Note how before he attempted to use blandishments to soften her character. Now he uses the technique of shame. He deliberately arrives late to his own wedding and, as Biondello reports, he hardly comes dressed appropriately:

Why, Petruchio is coming in a new hat and an old jerkin; a pair of old breeches thrice turned; a pair of boots that have been candle-cases, on buck-led, another laced; an old rusty sword ta'en out of the town armoury, with a broken hilt, and chapeless; with two broken points; his horse hipped, with an old mothy saddle and stirrups of no kindred...

His behaviour during the ceremony, which causes Gremio to refer to Katharina as a "lamb" and Petruchio as "the devil," reverses the behaviour of Katharina suddenly. Petruchio's insistence that he will not attend his own wedding banquet provokes a tantrum from Katharina, that gives Petruchio the excuse he needs to lay down the law:

I will be master of what is mine own.

She is my goods, my chattels; she is my house,

My household stuff, my field, my barn,

My horse, my ox, my ass, my anything...

Petruchio seems to be deliberately provoking Katharina in this scene therefore to whittle down her defences and "tame" her character to his "rightful" will as her husband. The ridiculous behaviour and preposterous conduct he employs is all an act for this purpose, and as we can see, it is beginning to have an effect.