This mishnah appears in the fifth chapter of Avos as mishnah 13, and in some versions it is mishnah 16. It states: "Arba middos b'nosnei tzedakah" - there are four types among those who give charity. A closer look at the mishnah reveals that two of the four do not give charity at all, so the plain reading is that we are not dealing with four givers here, but with four attitudes toward giving charity.
There are, however, those who understand that all four really are givers of charity, and there are two explanations of this:
The Alshich's explanation: Every Jew is compassionate and does acts of kindness, and by nature wants to do good for others. Therefore every Jew truly is a giver of charity; he simply has to overcome certain things that hold him back.
A second explanation: In earlier generations communities had the authority to compel their members to give charity. Consequently, even though these people did not want to give, in the end they gave, and so they are called givers of charity - only that their attitude toward the giving was poor.
"Harotzeh sheyiten v'lo yitnu acheirim":
The first one wants to give, but does not want others to give. He is concerned for the welfare of the poor of his community, but he wants to be the only person taking care of their needs, so that his name will be in the spotlight and he will receive the recognition. There are worse things in the world than this, but it is certainly not the ideal approach.
The Bartenura offers a different and fascinating angle: "d'yodea shetzedakah me'asheres v'ein rotzeh she'acheirim ya'ashiru" - he knows that giving charity makes a person wealthy, and he does not want others to become wealthy. He wants to be the only one who grows rich from the special power of charity, and so he wants to do it all himself.
An interesting point arises here regarding the terms 'ayin tovah' (a good eye) and 'ayin ra'ah' (a bad eye). Throughout the entire tractate these terms have not been explained as looking badly at another person: 'ayin tovah' means being happy with one's portion - a person is satisfied with what he has and views his situation in a positive light; and 'ayin ra'ah' means a feeling of insecurity about what he has, a sense that it is not enough. Yet according to the first explanation brought here, 'his eye is bad regarding others' means looking at another person negatively and being jealous of him.
The Bartenura therefore brings a second explanation, which does not interpret 'ayin ra'ah' as stinginess but as a feeling of insecurity regarding someone else's financial situation: "There is one who is more protective of his relatives' money than of his own, and even though he gives, he does not want his relatives to give, so that they should not lose their money." He wants to give because there is a worthy cause he wishes to support, but he feels insecure about his relatives' financial situation - his parents living on a pension, for example - and so he says: better that they hold on to every penny, and I will do it all myself. In this way he begrudges his parents a share in the mitzvah, out of concern that they do not have enough. According to this explanation, the use of the expression 'ayin ra'ah' is consistent throughout the entire tractate.
"Yitnu acheirim v'hu lo yiten":
The second one lets others give, but he himself does not give. His eye is bad regarding himself: he does not feel secure with the money he has, and so he wants to keep it all for himself and accumulate it, and does not want to give it away to others.
The commentators ask: why does this person get off so lightly? Seemingly this is the worse case - he does not give charity at all, and the most basic quality of a good person is to be a giver and to support others. Why, then, does the mishnah not condemn him as wicked, the way it condemns the fourth type?
In the end he does give; it is only his attitude toward the giving that is negative.
He would give if there were no one else giving; it is only because there are others who give that he lets them do it in his place. In other words, he does care about the welfare of the community and of those in need, but he cannot overcome his insecurity about his own financial situation - and if things reached an extreme, he really would give.
The Maharal does not accept these explanations, since someone who does not support the community and the needy is not a good person, and he has an obligation to get involved. The Maharal therefore explains that this person is plagued by insecurity when it comes to his own financial situation, but apart from that he takes an active part in supporting the community: he goes out and collects money, he attends to people's needs, he is on the phone raising funds for the charity fund. It is only he himself who does not give, because of his own financial insecurity. Such a person is not wicked at all - he does the right thing for the community in many ways, just not by way of giving the money he ought to give. His flaw lies in his attitude toward his own financial situation.
"Yiten v'yitnu acherim - chasid":
The third person wants to give, and also wants others to give. Not only does he supply the needy with what they lack, he wants others to give as well - so that the needy will not merely have their basic needs met, but will reach a comfortable situation. There is a great difference between someone who is not hungry and someone who is comfortable. He wants the number of givers to increase, because people need things and he wants to see people giving. Such a person is a chasid, and the Mishnah praises him.
"Lo yiten v'lo yitnu acherim - rasha":
The fourth person does not want to give and does not want others to give, and therefore he is wicked. This is cruelty of the highest degree. According to the way we understood the earlier Mishnah regarding the trait of Sodom, it is possible that this person falls into that very same category, if he objects on principle to giving charity.
In order to understand what such a person looks like, since he sounds like a caricature of wickedness, some point to his reasoning: if we build a strong charity system in our city and in our community, we will attract needy people, and there will be people walking around here dressed a certain way and having certain needs, and they will drain our resources. Better, then, to build a fence around the community and not establish strong charity institutions - that way the needy will go elsewhere, while we remain by ourselves in our closed community, comfortable, without having to see and deal with such sights. This person is still wicked, but he is a familiar type, not openly malicious and cruel - and nevertheless his words come from a terrible place.
The Midrash Shmuel notes that this same set of four traits applies to people with regard to Torah study as well:
There are those who learn and want others to learn too.
There are those who want all the honor for themselves.
There are those who do not want to learn at all, but want others to learn.
And since a person's attitude toward giving charity or refraining from it is more common and more relevant, and it is an issue that everyone in every community has to face, the Mishnah chose to focus specifically on it - even though the same applies equally to those engaged in Torah.
In summary: the message that emerges from the Mishnah is that every person needs to do what he is capable of doing. He must internalize that all his money comes from the Holy One, Blessed is He, and when he sees people in need - that is his opportunity and his privilege to help them. The joy gained from parting with a few dollars is incomparably greater than the joy gained from saving them.