Men and women who are discontented, though they enjoy many mercies from God, yet are unthankful for them...this is the vile nature of discontent, to lessen every mercy of God. It makes those mercies they have from God as nothing to them, because they cannot have what they want.
The graces of God's Spirit are nothing to a discontented heart who cannot have all that he would have. God has given you health of body and strength, and has given you some competence for your family, some way of livelihood, yet because you are disappointed in something that you would have, therefore all is nothing to you.
The Spirit of God extenuates evils and crosses, and magnifies and amplifies all mercies.
Discontent takes away the present comfort of what you have because you have not something else. What a foolish thing is this, that because I have not got what I want, I will not enjoy the comfort of what I have! God gives you many mercies, but you see that others have more mercies than you and therefore you cry for more; but God does not give you what you want and because of that you throw away what you have - is not this folly in your hearts? It is unthankfulness.
--Jeremiah Burroughs, The Rare Jewel of Christian Contentment