He said to them, "Because of your little faith. For truly, I say to you, if you have faith like a grain of mustard seed, you will say to this mountain, 'Move from here to there,' and it will move, and nothing will be impossible for you."
Matthew 17:20 ESV
Faith must always be present! Without faith, it is impossible to please Him. If repentance and faith is our response to the Gospel - in which the grace of God redeems us from eternal destruction, then certainly, we shall have enough faith; small as a mustard seed (at least) in our Lord when it comes to our petitions.
A common misconception about this verse is: you will have everything you request before God answered the exact way you asked it, no matter what you ask as long as you have faith. This, however, is not the case.
Much clarity is provided when we refer back to the story where Shadrach, Meshach, and Abednego are refusing to bow down before king Nebuchadnezzar's statue and are facing, what seems to be, inevitable death. Their final response before being thrown into the furnace is as below:
"If this be so, our God whom we serve is able to deliver us from the burning fiery furnace, and he will deliver us out of your hand, O king. But if not, be it known to you, O king, that we will not serve your gods or worship the golden image that you have set up."
Daniel 3:17-18 ESV
These three men did not know, at the time, whether God would save them. But their faith was evident by understanding that God is able, and His will is sovereign.
All things work together for the good of those who love Him. However, we must not presume what that looks like.
God listens and answers to our petitions. After all, He says "ask and you shall receive". However, we must understand that God is able and God is sovereign. His character never changes. His will shall come to pass and we shall trust Him no matter the circumstance.