"Do unto others as you'd have others do unto you." Matthew 7:12

In other words:

It helped to act for others likewisely: as we need, as they need.

Why? I think it's because if we trust someone (with giving) reasonably on average this came back to us somehow and may be expected to.

"Be fruitful and multiply." Genesis 1

In other words:

We should contribute to life, especially via our talents.

We could multiply with children and should if it's time, if life could bear them. We could also multiply our efforts with teamwork.