Did you know that Amazon.com occasionally sells products at a loss? It's true. They occasionally have items that they sell at a slight loss. If it costs them $10.00, they sell it for $9.50, losing $0.50 on each sale.
Why do they do this? Because they hope that customers who are attracted by that inexpensive price will be lured into putting something else into their shopping cart before they check out. And even if they don't buy something else, they've made one purchase, and a customer who has made one purchase is more likely to come back and make another later on.
It's an ulterior motive.
I do the same thing. One of my game websites has some free games. Why? It is my hope that people who come back day after day to play the free games will sooner or later say, "I wish I could play those other games," and then pay the subscription fee for the site.
It's an ulterior motive.
Ulterior motives are okay in the business world; it's part of what makes our system of business work. But ulterior motives have no place in the world of the church and the followers of Christ.
When Jesus's disciples were arguing about who was greatest (pick a passage, any passage -- this appears to have been a common argument!) Jesus said to them:
It would be easy for us to think "Oh! I'll be a servant, so I can be great!" But servanthood is not something we take on for the sake of gain; servanthood is, in itself, true greatness. Because servanthood is part of the character and nature of Christ (see Philippians 2:1-8)
Why did Jesus leave the glory of heaven for this miserable, broken world? It was not because he would one day be exalted for his service (see Philippians 2:9) but because of His great love for us.
So it must be with us; I shouldn't serve with an ulterior motive, seeking greatness in this life (if I do, I might be disappointed!). I should serve because of my love for Christ, because of my love for my fellow man, and because I desire to have the mind and attitude of Christ.