Complex sentence: The Nitrogen is now attached to the 2 position of the chain; its lone pair again attacks the carbon of the other carbonyl, joining the chain, and again protonating the oxygen and deprotonating the nitrogen.
Split into simpler sentences: The Nitrogen is now attached to the 2 position of the chain; its lone pair again attacks the carbon of the other carbonyl. Again joining the chain, protonating the oxygen and deprotonating the nitrogen.