Having freedom means living with a purpose. It makes no sense to move aimlessly in life. Every good athlete has a purpose to every move he or she makes.
To stay salty is to live out the beatitudes. To be salty is to be like Christ. When we do that we help people around us develop a taste for Christ and be attracted to Him.
Jesus wants us to understand that our love and obedience to Him should have nothing to do with other people.