"Wherefore if God so clothe the grass of the field, which today is, and tomorrow is cast into the oven, shall he not much more clothe you, O ye of little faith?"
“Wherefore, if God so clothe the grass of the field,”
Jesus is the one who makes the wildflowers grow. He sees to it that His flora bloom when and where He has planned. The herbs and grasses though very transient, are given life and all they need by Him.
“And why take ye thought for raiment? Consider the lilies of the field, how they grow; they toil not, neither do they spin: And yet I say unto you, That even Solomon in all his glory was not arrayed like one of these” (Matthew 6:28-29).
“Which today is, and tomorrow is cast into the oven,”
The grass which stokes the eastern cooking ovens is not of significant monetary value, and yet He cares for it. One day it is in the field in glorious bloom, the next it’s dead and dried, put into the oven to bake bread.
“Shall he not much more clothe you,”
Surely, you are more important than grass! Your needs are your Heavenly Father’s concern. If He cares for the field grass, don’t you think He will care for your need?
“O ye of little faith?”
Jesus used this phrase four times in His teaching. Each time He said this He was rebuking some incorrect facet of the disciple’s faith. He used these problematic events in their lives to help grow their faith and keep their eyes focused on Him.
Jesus rebuked their fear; 
“And he saith unto them, Why are ye fearful, O ye of little faith? Then he arose, and rebuked the winds and the sea; and there was a great calm” (Matthew 8:26).
Jesus rebuked his doubt;
“And immediately, Jesus stretched forth his hand, and caught him [Peter], and said unto him, O thou of little faith, wherefore didst thou doubt?” (Matthew 14:31).
Jesus rebuked their reasoning.
“Which when Jesus perceived, he said unto them, O ye of little faith, why reason ye among yourselves, because ye have brought no bread?” (Matthew 16:8).
Jesus rebuked their care.
“If then God so clothe the grass, which is today in the field, and tomorrow is cast into the oven; how much more will he clothe you, O ye of little faith?” (Luke 12:28, parallel to Matthew 6:30).
These four things: fear, doubt, reasoning, and care, will cripple our faith if we let them take root in our minds. Believers, no matter your difficulty, keep your focus on the Lord, trust in Him, He always does what is right.
 These four thoughts of Jesus using the phrase “O ye of little faith,” are from E.W. Bullinger, The Companion Bible, the electronic version in eSword.