Usually when you hear this, you hear it in a negative sense. What I want to do is look at it from a positive perspective.
Lets read some scriptures:
Luke 6:38 Give, and it will be given to you. A good measure, pressed down, shaken together and running over, will be poured into your lap. For with the measure you use, it will be measured to you."
2CO 9:6 Remember this: Whoever sows sparingly will also reap sparingly, and whoever sows generously will also reap generously.
What do these passages tell you? It tells us in plain words that you get what you give. If you give a little, you get a little. If you give a lot, you get a lot. In other words it is up to us. So if we remember this in a positive sense, what does it mean? If you want good things to happen to you, you have to do good things for others. I think that is pretty simple.
Lets look at it a little deeper:
2CO 9:7 Each man should give what he has decided in his heart to give, not reluctantly or under compulsion, for God loves a cheerful giver.
MT 6:1 "Be careful not to do your `acts of righteousness' before men, to be seen by them. If you do, you will have no reward from your Father in heaven.
What we give needs to come from the heart. If we do things just to get or to show people what all we do, we will not get any reward. In other words our motivation has to be right. So you say: "Okay, I want to help others, but I just can't afford it."
Maybe you can not afford to help with money, but hear this:
2CO 9:8 And God is able to make all grace abound to you, so that in all things at all times, having all that you need, you will abound in every good work.
He gives you what you need to do the job. If money, then money, if other then other. In other words you don't need to necessarily help with money. If you ask God, he will tell you what you can do.
Another reason to give:
PR 19:17 He who is kind to the poor lends to the LORD, and he will reward him for what he has done.
In other words, if you give to the needy you are actually giving to God and he promises to reward you for it. It backs this up in Matthew:
MT 25:40 "The King will reply, `I tell you the truth, whatever you did for one of the least of these brothers of mine, you did for me.'
If this doesn't motivate you to want to help others, I don't know what will. This also applies to our salvation: We are in control of our future.
GAL 6:7 Do not be deceived: God cannot be mocked. A man reaps what he sows. 8 The one who sows to please his sinful nature, from that nature will reap destruction; the one who sows to please the Spirit, from the Spirit will reap eternal life. 9 Let us not become weary in doing good, for at the proper time we will reap a harvest if we do not give up. 10 Therefore, as we have opportunity, let us do good to all people, especially to those who belong to the family of believers.
This actually ties the doing good physically to the spiritual. It also tells us that the way we live our life has a direct influence on our eternal life. The reward may not come immediately as the scripture shows. Also the reference to growing, makes me believe it refers to it not necessarily being immediate gain.
Think of it like building your retirement fund:
MT 19:28 Jesus said to them, "I tell you the truth, at the renewal of all things, when the Son of Man sits on his glorious throne, you who have followed me will also sit on twelve thrones, judging the twelve tribes of Israel. 29 And everyone who has left houses or brothers or sisters or father or mother or children or fields for my sake will receive a hundred times as much and will inherit eternal life. 30 But many who are first will be last, and many who are last will be first.
So what is our conclusion?
I believe the way we treat others and what we do for them will have a direct influence on our everyday life. It will make life a lot better and a lot more rewarding. It will also make a difference in our eternal life. God promises a return of one hundred times what we put in. The Bible says that we should store up treasure in heaven and I believe this is what it is talking about. We will later be rewarded for what we do now.