To have a giving heart like God means to look out for the well being of others. We give not to receive a reward today, but we know that God will reward us in the future for our faithful life as He sees fit.
While we should never live our Christian life just to accumulate rewards, we should know that God has given incentives and rewards to help us strive deeper into the Christian life. The believers in the hall of faith (Hebrews 11) are excellent examples of this type of life.
Even though the people of Israel found themselves without hope in their situation and even though we might find ourselves without hope today, God fulfilled His promise of sending a King who would rule in righteousness.