How can one prepare for a negative change of fortune?

(30,12) When you take the sum of the children of Yisrael according to their numbers, each one shall give (ונתנו) an atonement for his soul to Hashem when they are counted.

Behold, the cantillation notes on the word ונתנו are קדמא ואזלא, which mean precede and go. We can explain that they come to allude to the teaching of Chazal in the gemara Shabbos 151b - Said R. Chiya to his wife: When a poor person comes, be quick to give him bread, so that others may be quick to bring to your children. She responded: You are cursing them! He replied: It is a wheel which revolves in the world.

Now, the word ונתנו can be read fowrards and backwards, because someone who gives sometimes needs others to give to him, G-d forbid. This is what the notes allude to: Precede quickly to bring bread to a poor person, in order that others will precede quickly to bring to your children. קדמא - precede quickly and give him, ואזלא - and let the mitzvah of Tzeddakah go before you, before the wheel of fortune revolves on your children.

How much charity can one give?

(30,15) The rich shall not give more, and the poor shall not give less.

Behold, the notes on the words "the rich shall not give more" are מונח רביעי. We can explain that this comes to allude to the teaching of Chazal in the gemara Kesuvos 50a - one who is lavish in his giving of charity should not give more than a fifth of his wealth.

This is the allusion of מונח רביעי (leave four). That even a rich person should give more than a fifth. He should leave four parts for himself, and give away the fifth part.