how flash memory/SSD write dta internally?

I was reading a book which says:

a flash memory consists of a sequence of B blocks, where each block consists of P pages.Data are read and written in units of pages. A page can be written only after the entire block to which it belongs has been erased (typically, this means that all bits in the block are set to 1). However, once a block is erased, each page in the block can be written once with no further erasing.

I’m confused wht the saying of

"once a block is erased, each page in the block can be written once with no further erasing."

Does it mean that once we write data to a block, then this block can only be read-only from now on? because according to what the author says, if you want to write data into a page, the block containing it needs to be erased first, since the block had been erased and cannot be erased for a second time, then this block is read-only?