Lenni provided readings and insight:
To better understand the power of gratitude, I found these two experiences of Jesus as helpful: In Matthew 15:29, Jesus feeds 4,000 people with a few loaves and fishes. "And he took the seven loaves and the fishes, and gave thanks, and brake them, and gave to his disciples, and the disciples to the multitude. And they did all eat, and were filled."
Then in Mark 11: 20, Jesus is hungry and looks for figs on a fig tree but it wasn't the season for figs. However he rebukes that tree and the next day it is withered to the root. His disciples remark upon this and Jesus tells them: "Therefore I say unto you, What things soever ye desire, when ye pray, believe that ye receive them, and ye shall have them."
Jesus expressed gratitude in the face of what appeared to be inadequate supply because he clearly saw that God is the source of all supply, not matter - and that God's abundance, like God, is present and available every moment. Likewise, he rebuked the claim that there wasn't supply present to fill his need (as with the fig tree). This is the claim of animal magnetism that insists there are valid reasons why supply and demand aren't in perfect balance.
In Science & Health, Mrs. Eddy explains the feeding of the multitude: "In the scientific relation of God to man, we find that whatever blesses one, blesses all, as Jesus showed with the loaves and the fishes - Spirit, not matter, being the source of supply." (What a wonderful rebuttal of all the income inequality, glass ceiling, etc., arguments and the divisiveness lurking behind them.)
Similarly, when the opposite claim presents itself we must rebuke it like Jesus did: "Rise in the conscious strength of the spirit of Truth to overthrow the plea of mortal mind, alias matter, arrayed against the supremacy of Spirit."
Gratitude and joy serve as powerful acknowledgement of the constant, conscious presence of God - and that brings healing in the face of disease or discord.