But don’t act like them. If you want to be great, you must be the servant of all the others. And if you want to be first, you must be the slave of the rest. (Matthew 20:26-27 CEV)
What is the greatest commandment? It is to love God with your whole self; body, spirit, mind and strength. The second is to love your neighbor as yourself. All commandments fall in these commands to love. To love is to serve the one you love. True love is sacrificial. It is not self serving. It is not selfish. Since love is the greatest virtue, it follows that the one who serves is greatest than the one being served.
It is more prominent in the Church setting. The leaders serves, they are servant leaders. Leaders cannot be proud because they are, in fact, humble servants. This title strikes a balance so that no leader abuses his position and at the same time gains the respect of the brethren.