“Then Jesus answered and said unto her, O woman, great is thy faith: be it unto thee even as thou wilt…”  
Matthew 15:28

With great faith, it will be unto you even as you will:
“The LORD is my shepherd; I shall not want.”  Psalm 23:1
Faith comes by hearing the word, and so receiving the word to abide in you is the way to get all of the desires of your heart:
“If ye abide in me, and my words abide in you, ye shall ask what ye will, and it shall be done unto you.”  John 15:7
With faith, you fight! You insist; little faith would easily give way when there’s a seeming setback, but great faith would insist and prevail just like a small car would easily give way in front of a truck.
“Fight the good fight of faith…”  1Timothy 6:12
Peter walked on water because of the word of Jesus (that’s faith) but immediately he was met with a challenge, he gave way (that’s LITTLE faith):
“And immediately Jesus stretched forth his hand, and caught him, and said unto him, O thou of little faith, wherefore didst thou doubt?”  Matthew 14:31
In the main verse, the woman went to Jesus for her daughter’s deliverance (that’s faith), was ignored by Jesus, was almost chased away by his disciples, even heard Jesus seem to refer to her as a dog, but she insisted, she didn’t give way (that’s GREAT faith):
“But he answered and said, It is not meet to take the children’s bread, and to cast it to dogs. And she said, Truth, Lord: yet the dogs eat of the crumbs which fall from their masters’ table.” Matthew 15:26-27
Great faith insists and win!