Yes, Lang is severely lacking there. Now to fully understand it, you will need an analysis book. But depending on the rigor, there are several options.
On the rather elementary level, I recommend Keisler:
https://www.math.wisc.edu/~keisler/calc.html Keisler covers two very different approaches to limits: the standard epsilon-delta approach, and the infinitesimal approach. Both approaches really help understand the concepts.
Somewhat more advanced, there's good books like Nitecki's calculus deconstructed and Apostol's calculus. Those are somewhat closer to being analysis books, but they still qualify as calculus. After that, there's analyis.