Why should Christians give to others?
Giving to God is a great privilege. When we give we are showing Him our gratitude for giving us eternal life and being chosen to serve Him. We are also demonstrating our reliance on Him to meet all of our needs. He knows what we will do before we are born. When we give we do not prove our reliance on God to Him, we prove to ourselves and to those around us how much faith and trust we have in Him.
When we give to the poor we are also trusting in God to meet our needs. He promises to meet all of our needs (not our desires) in this life (Matthew 6.33-34), and to reward us in the life to come. Giving to the Lord and to the poor is a way of laying up treasure in heaven (Matthew 6.19-20).
It is important to remember that giving to the poor and needy can be an advantage. The time may come when you may have need of assistance from others. Those who you helped may help you (Luke 16.1-9).