Freedom inherently refers to a past for there must be a freedom from something that was in bondage and is not anymore. Adam and Eve relied on God to be their guide and provider and teacher and more but as that terminated through disobedience they had to rely on their wits and instincts and what they saw around them. It made them a prisoner to themselves.
It's like traveling through a giant jungle with a guide. The guide leads me through and I fully trust him In every way. Suddenly he disappears and I find myself alone. Though my surroundings have not changed, I am now lost and need to rely on my instincts to survive. I have become a prisoner in this jungle.
This freedom (to serve) is a freedom from self. When we were servants to self, our purpose and existence was to watch out for me. It wasn't safe anywhere; everyone was out to get me; there was never enough; No one cared for me and no one trusted me and no one believed in me and no one respected me; it was survival of the fittest.
I believe the freedom to serve has reversed the reliance on self. Now God is my security and defender. He is my provision. He is my counselor.
Furthermore, serving flows from love which will never seek its own. Love is not selfish. It is not self serving. Free to serve means free from self love.
The sum of the commandment is to love God above all and your neighbor as yourself.