There are many answers but one that came to mind comes from a book called Passport to the Land of Enough by Joel Nagel, who has led the Lansing Area Church of Christ in Michigan since 2002. It is an incredible book that leads you to experience life as a disciple in other countries. By adopting the way others live, a heart for missions is nurtured and the heart overflows with gratitude and joy. I have spoken with several couples about how they have been able to sell possessions and give to missions, not because they have to but because they have enough and don't need more.
As 1 Timothy 6:6 says, "godliness with contentment is great gain." If you are looking for God to revive your heart to reach the world, this book will lead you there. You can find it here.