All the sinful states of our hearts are owing to unbelief in God’s super-abounding future grace. All our sin comes from failing to be satisfied with all that God is for us in Jesus. Misplaced shame, anxiety, despondency, covetousness, lust bitterness, impatience, pride — these are all sprouts from the root of unbelief in the promises of God.
… the heart that loves money is a heart that pins its hopes, and pursues its pleasures, and puts its trust in what human resources can offer. So the love of money is virtually the same as faith in money — belief (trust, confidence, assurance) that money will meet your needs and make you happy. Love of money is the alternative to faith in future grace. It is faith in future human resources. Therefore the love of money, or trust in money, is the underside of unbelief in the promises of God. Jesus said in Matthew 6:24, “No one can serve two masters… You cannot serve God and mammon.” You can’t trust in God and in money at the same time. Belief in one is unbelief in the other. A heart that loves money — banks on money for happiness — is not banking on the future grace of God for satisfaction. – John Piper, Future Grace