The purpose of the lectures is to focus attention on the course objectives and to facilitate the achievement of those objectives. The course objectives are to present the modern aspects of the science of chemistry and in particular to begin to understand and appreciate the relationship between the structure of a molecule and its chemical and physical behavior.
Frequently, material is presented in lecture in greater depth than in the textbook (or even missing from the textbook) so as to assure either a better understanding or to stimulate questions that might not otherwise have arisen. At other times, the multimedia technology enables presentation of a complicated illustration from the textbook by assembling the illustration piece by piece. And there will be ventures with applications to show the relevance of the course material to other fields, to scientific method in general, and to everyday life.
On the practical side, it is not rare for the instructor to point out during a lecture that "you should really know how to do this", a phrase that hints at possible exam material.
Of course, the lecture environment also provides an opportunity to ask relevant questions, which is encouraged.