Luke 17:5-10  The request of the disciples is reasonable and good, " Increase our faith!" 
Faith, so that we can forgive others, so that we won't be stumbling blocks or be the ones who stumble.  But, Jesus answers in a way that .... well, frankly, doesn't answer that request.  He doesn't grant them bigger faith with a touch of His hand... instead He teaches them this:

"If you had faith like a mustard seed, you would say to this mulberry tree, 'Be uprooted and be planted in the sea; and it would obey you."  If you have faith - conviction, reliance on Christ, assurance, belief, fidelity; constancy in the Truth...  Then, the tree would obey... it would conform to your authority, submit to your command.

Then, Jesus gives them a parable of a master and his slave.  The slave comes in from his work, either tending sheep or plowing in the field.  The master does not have the slave come in and sit down and be served.  No,  the slave is then required to do the rest of his assignments - prepare food for the master, clothe himself properly and serve the meal.  When he is finished with this, then he can eat his own supper.  The slave does what he has been commanded to do.  The master doesn't thank the slave for doing his job.  It is expected and required.

Verse 10 - " So you too, when you do all the things which are commanded you say, 'We are unworthy slaves; we have done only that which we ought to have done.' " 

 According to the Bible Knowledge Commentary this teaching is about responsibility - the disciple of Jesus is responsible to have faith - and is also responsible to serve God humbly, without the need for "special praise from his master for doing his job."  Matthew Henry adds this thought, " As with God nothing is impossible, so all things are possible to him that can believe. Our Lord showed His disciples their need of deep humility.  The Lord has such a property right in every creature, as no man can have in another, he cannot be in debt to them for their services, nor do they deserve any return from him."

So... we belong to God, our Creator, our King, our Master.  His command to us is to have faith. It is our responsibility to trust Him, to exercise the faith that we have, humbly obeying Him.  That is our expected service as His slaves. Do we believe that everything is possible with Him?  Do we believe that He has the authority to grant us authority?  If we do then we can ask for the impossible and there will be compliance with our command...

That is ... well... a big step of faith!
That's the point, isn't it?

Father in Heaven,  Almighty in power and in dominion and glory.  All things are possible for You!   I am Your unworthy servant, Lord.  Complete the work in me that You desire to do.  Help me to live and walk in faith, according to Your will.  I ask this Jesus in Your Name. Amen