The profile file located in /etc is read automatically by everyone when they log in. This file will generally contain:
global or local environment variables;
security commands; and
message of the day or disclaimer information.
Here’s a brief explanation of the above points.
Certain global environment variables are set so that users and their shell processes and applications can have access to them.
PATH holds the location of directories containing executable, library, or just plain files so that you locate them quickly.
Terminal settings lets the system know about the more general characteristics of your terminal.
Security commands will include file creation modes, or double login prompts ...