The primary purpose of the Legion is the sanctification of its members.
This is achieved by personal service.
In Legion service when we interact with people, "The person of Jesus is once again seen and served by Mary His mother."
Mary ensures we receive the grace necessary to approach the work with the proper spirit.
Being of service to people is an expression of love for them. It is in this way we obey the commandment to love our neighbor. In doing service our ability to love grows. This is how the Legion achieves its goal of personal sanctification of its members.
There is no greater service we can do for people than to bring them to salvation through Jesus.