Some translations set each line of poetry farther to the right than the rest of the text to make it easier to read. The ULB does this with the poetry that is quoted from the Old Testament in 2:6, 7, 8, and 22. The ULB also does this with the poetry in 2:10.
Peter uses a building made of large stones as a metaphor for the church. Jesus is the cornerstone, the most important stone. The apostles and prophets are the foundation, the part of the building on which all the other stones rest. In this chapter, Christians are the stones that make up the walls of the building. (See: [[rc://en/ta/man/jit/figs-metaphor]] and [[rc://en/tw/dict/bible/kt/cornerstone]] and [[rc://en/tw/dict/bible/other/foundation]])
When Peter tells his readers to "long for pure spiritual milk," he is using the metaphor of a baby craving his mother's milk. Peter wants Christians to crave God's word the same way a baby craves milk. (See: [[rc://en/ta/man/jit/figs-metaphor]])