Such sentences may have different meanings in specific paragraphs, but it is not difficult to understand only from the original intention.

It may explain that mathematics is a very logical subject. Once a point is broken, it is impossible to understand the subsequent content, because the conceptual algorithm and derivation of the subsequent content often refer to the previous knowledge.

For students who are already weak in mathematics, it is possible to stop directly if they don't understand it once. If you have a solid foundation, this will not happen. You can make up after class.