Some translations set poetry farther to the right than the rest of the text to show that it is poetry. The ULB does this with the poetry in verses 1-8.
The Book of Revelation often describes heaven as a place where people sing. They worship God with songs. This illustrates that heaven is a place where God is always worshiped. (See: [[rc://en/tw/dict/bible/kt/heaven]])
The wedding celebration or feast is an important image in Scripture. Jewish culture often pictured paradise, or life with God after death, as a feast. Here, the wedding feast is for the Lamb, who is Jesus, and his bride, who is all his people.