Mathematical logic includes propositional calculus, predicate calculus and axiomatic set theory. Set theory is the basis of all branches of mathematics. But without the knowledge of propositional calculus and predicate calculus, it is impossible to study and develop set theory. However, if you don't specialize in mathematics, if you only need the superficial knowledge of simple set theory, you don't need to go deep into mathematical logic. Most science and engineering students don't have to study propositional calculus and predicate logic, or just click on it.