The temptation to selfishness is one of the great snares of Christian service: the more you serve the stronger the temptation grows. It is harder than it seems to keep one's spiritual zeal protected from one's ego.
Everyone - Christian and non-Christian alike - appreciates attention. ("I love anonymity / and I love being noticed / just the same as anybody else..."*) Because of this, there is a strong tendency to focus on those areas of service where we are more likely to receive the attention that we crave. This can be dangerous. If those areas are not in line with what God would have us doing, we're headed for trouble.
Spiritual work without divine empowerment = exhaustion. Plain and simple. When we kick against the persistent direction of the Lord in order to attract artificial attention, we will promptly wear ourselves down to nothing. Yes, "I can do all things through Him who strengthens me." And the contrapositive is also true: "Apart from me you can do nothing."
The basis of Christian service must always be Jesus Christ, for the simple reason that nothing else is worth it. All too often, we're distracted from just loving the Lord and begin to fuss and fret about all the work we have to do and how tired we are and on and on and on. We forget that to obey is better (and more restful) than sacrifice, and before you know it we're booking passage to anywhere but Nineveh.
I don't know about you, but I can really sympathize with Martha sometimes. "Sometimes we forget to give to the Lord / 'cause we're so busy giving somewhere else..." It's so easy to get caught up in the intoxicating "commotion of devotion." But it is only in ministering directly to Jesus that we find peace, fulfillment, and rest.
*Caedmon's Call, Long Line Of Leavers, "Ballad of San Francisco"
Scriptures cited: Acts 26:14, Phil. 4:13, John 15:5, 1 Sam. 15:22, Luke 10:38-42