There is an absolute correlation between faith in the promises of God and peace of mind in giving away what we may think we need but don't:  "Let your character be free from the love of money, being content with what you have; [why? because of a promise] for He has said, "I will never desert you, nor will I ever forsake you."                                                                                                           (Hebrews 13:5)

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...Let the glorious promise of God strengthen your faith: "My God shall supply all your needs according to His riches in glory in Christ Jesus," (Philippians 4:19).

John Piper