“Any fool can know. The point is to understand”. Safety talks are opportunities to pass on knowledge and understanding. Safety talks discuss an activity and then how to safely handle the task. For example working at heights. Understanding that fall protection need be in place and what types of fall protection are known to be safe helps understanding. But safety talks also support the opportunity for questions to be raised which helps clarify understanding.
Safety talks also serve another purpose. From my experience, most workers know what is safe and unsafe behavior but getting reminders in the form of a safety talks helps remind them of all the safety steps to avoid the hazards of a task. Safety talks also show employees that the company/management takes safety seriously and supports employees following safety practices in the workplace.
Safety talk subjects can be accessed on the OSHA web site for ideas. https://www.osha.gov/SLTC/text_index.html