God sometimes gives us promises, and often call us to be and do things for His Kingdom. Often those things require great risk and cost. Sometimes we think, "I can just do that later, " or, "this is too hard, I can't do this anymore." When we do that we act like the Israelites on the edge of the promised land and put our part in the promise in jeopardy.
Now is the time to be faithful and follow-through, because we may never get another chance.