When you look at someone who is humble and serving, out of love, and then you look at someone who is just a doormat for others to use and walk-on, sometimes it is hard to see the difference from the outside. Both of them do things in service of others. Both of them put themselves aside, it seems.
But here's the difference. The person who is a doormat is a person who is dominated by fear and who seeks to control the outcomes, such as gaining approval, preventing rejection, and maintaining the status quo, by putting on a compliant, lower-than-others, people-pleasing facade. Whether they realize it or not (most of the time they do not, it is unconscious), it is a controlled position of avoidance... avoiding their true selves and avoiding the potentially painful consequences of rising up and being geniuine and seeking to connect with others eye-to-eye (they might reject or hurt you, after all!). It is masqueraded anger, a way to deal with perceived threat by flight and control. It is the equivalent of locking yourself behind a wall and while accepting abuse and lobbing gifts over the wall to control others and keep them from walking away from you. Sure, it might seem "safe", but at what cost? At the cost of yourself and any possibility of having closeness and engagement with anyone in this world.
Jesus served out of true humility (see Philippians 2). His service was not a veiled power-play against His Father or others, a veiled way to keep the world going the way He desperately demanded it to be while staying at a controlled and emotionally "safe" distance. It was not a way to deal with potential threat. He engaged, he let go, he did not count his equality with God something to be held onto, he faced the risks and the pain he knew would come. In the garden, Jesus said to His Father, "Nevertheless, not my will but your's be done..." He is free, He is Himself, and in that freedom He chose to give Himself.
See, there is a way to serve others that is really only to placate them and keep them at a safe distance, managing the perceived threat, thinking that if you appease them you can be safe in your little emotional cocoon. That is what doormats do. They bury and imprison and punish all the parts of themselves that might cause conflict or break up the status quo or lead to being abandoned, they turn against themselves as a way to manage the pain and uncertainty of this world. But there is a way to serve others that involves throwing caution into the wind and engaging life and connecting with others, putting aside your own safety for the sake of the good of others. That is what Jesus did.