“Now to him that worketh is the reward not reckoned of grace, but of debt.”
Romans 4:4

He means it when he says don’t let your heart be troubled, instead rest in his love and in his grace, the Apostles had complained about having limited amount of resources:
“And they reasoned among themselves, saying, It is because we have taken no bread.” Matthew 16:7
And Jesus wasn’t very pleased with their way of thinking, he thought (even though they misunderstood what he said originally) because he was with them, they should have known that he could provide for them even if they had not carried enough for their sustenance:
“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
They let their shortcoming make them ignore God’s present ability in that situation, so he reminded them of what he had done before to make them aware of what he could do- Matthew 16:9-10
This is one of the reasons to go through the word, to see his grace at work in the lives of others so you would be inspired to believe that the same grace would be manifest in your life:
“For whatsoever things were written aforetime were written for our learning, that we through patience and comfort of the scriptures might have hope.” Romans 15:4

Bible Reading Plan: Pslams 110,111 and 2 Samuel 17,18