Do not be deceived, God is not mocked; for whatever a man sows, this he will also reap. For the one who sows to his own flesh will from the flesh reap corruption, but the one who sows to the Spirit will from the Spirit reap eternal life. Let us not lose heart in doing good, for in due time we will reap if we do not grow weary. So then, [a]while we have opportunity, let us do good to all people, and especially to those who are of the household of the faith. (Galatians 6:7-10) Read the whole chapter here.
You reap what you sow. Sometimes the reaping comes quickly. Sometimes the reaping comes late. But the reality remains the same: the reaping will come.
While you have the opportunity, as a Christian, you should be sowing good seed. You have a limited amount of time on this planet. The sowing you do while you are here can be reaped for eternity. The seeds you sow can literally change someone else's eternity.
The challenge for all Christians is to sow kindness into your neighbor's life; to sow love into a lost friend's trial; to sow generosity into your local church. The seeds you sow today may be reaped tomorrow or 25 years from now, but the law remains that it will be reaped, and someone's eternity can be changed.