What is the one most important thing about ministry and service to others?

The single most important thing besides Christ Himself, is love. In Romans 9:3 we read that Paul was willing to lose his life, both in the natural and for eternity, so that his people would no longer be separated from Christ.
I have often heard a great number of leaders and servants tell about their devotion to Christ Jesus. I have head of their stories of great works and success. Yet most of these have never lost their lives, they have only gained a greater reputation, more wealth, bigger fan club, TV, radio and internet following.
At the same time there are those who become as “one with no reputation” and fulfill every desire of God for them. The second serve out of obedience motivated by love. The first do out of trying to earn righteousness based on works. They are in danger of not even entering eternity themselves. (This is not intended to be self-righteous judgments as if I have the right plan. It is intended to be a call of compassion to the body of Christ for the body of Christ. Some need to decrease so that others can increase. All of God’s children need a place in the body).
The point is not how successful you are, but how loving you are. God is the one who both gifts and calls. If you do great things that you were never called to do, you have robbed another member of the body of Christ, disobeyed God by not doing what He called you to do and sought to establish a righteousness greater than grace. While in America self success is rewarded, it will not be in the Kingdom of God. It is God’s plan that we follow Him together. He is the head. And while we love leaders and those with divine authority just as much as we love the homeless, the socially challenged, the poor, the uneducated and our enemies; we do not serve success. We serve the Lord.
So what is the motivation of your heart? Do you want to write a book, lead worship, fast and pray so that you increase in your significance? Do you want to defeat the world by self promotion of your godliness? That won’t work. The only place to stand is in God’s calling of you (Rom. 9:11). You cannot make your own way, for He is already the way.
Please note that this does not mean that we do not strive, labor, work, study, increase in wisdom and education. But we do the natural things of improvement because we love, not because we are seeking to be lovable or significant. We work hard at our calling and work hard at joyfully staying within its limits.
Take it from a guy that has sought for years to be something. The more you run away from the simplicity of devotion to Christ Jesus, the more you run into frustration, trouble, critical spirits, being judgmental and false righteousness. Enter the rest of the Lord and give up the rat race.