Serving others is an extension of serving God. They aren’t two different things. When you are serving God by serving others, there is no burnout, no resentment at the lack of gratitude. There is fatigue and weariness. There is struggle, but there is fruit, especially in your life. If serving others is making you more like Jesus, if it’s producing the fruits of the Spirit in you, then you are serving God. If serving others is taking away your joy, your peace, your patience, etc., then you are serving yourself.