Two explanations of the Chumash’s reference to the day’s warmth
The first passage of the parasha begins by telling us that Hashem appeared to Avraham. The Chumash does not seem to explicitly describe the nature of Avraham’s vision. This omission is the foundation of an extensive discussion and debate among the commentaries. The passage continues by relating that the events being described occurred as the day grew warm. Then, the passages describe Avraham’s encounter with three travelers. Avraham sees the travelers and beseeches them to briefly pause from their journey and allow him the privilege of hosting them in his home. They agree to Avraham’s request.
Our Sages note the unusual reference in the first passage to the weather. Why does the passage mention that the events unfolded as the day grew warm? Rashi quotes one of the responses. These events occurred while Avraham was recuperating from his recent circumcision. Avraham was always eager to entertain travelers and share his home with them. Hashem wanted to assure that Avraham was spared the burden of caring for guests during his recuperation. Therefore, Hashem caused the sun to wax in order to discourage travelers.
Of course, our Sages realize that this explanation for the Torah’s reference to the hot weather is contradicted by the very next passage. Three travelers appear before Avraham. As the narrative unfolds, it becomes clear that these travelers are messengers of Hashem. Why did Hashem increase the intensity of the sun to save Avraham from the burden of caring for travelers and them send three travelers? Rashi explains that the Sages resolve the contradiction. Hashem wished to relieve Avraham from the responsibility of caring for guests. But Avraham responded with disappointment. He wanted to be able to offer his hospitality to travelers, but because of the intense, heat the roads were abandoned. In order to appease Avraham, Hashem sent him His own messengers to whom Avraham would extend his welcome. 
Rashi’s comments are drawn from a discussion in the Talmud.  The Midrash is also troubled by the Torah’s reference to the weather but offers a different explanation. It explains that the warmth of the sun is an agent for healing. Hashem brought forth the sun’s warmth to assist Avraham’s recovery.  The appearance of three travelers sent by Hashem does not contradict this explanation and requires no explanation. In other words, Hashem provided Avraham with the warmth of the sun to aid his healing and three messengers to share a message with Avraham.
If these two explanations are compared, it seems that the Midrash’s account for the description of the weather is the easier to understand. The Talmud’s explanation seems needlessly convoluted by comparison. According to the Talmud’s explanation, Hashem first brings forth the sun in order to discourage travelers and then realizes that the absence of travelers will disappoint Avraham. Hashem then adjusts His plan and sends His own messengers to visit with Avraham. The Midrash’s explanation is simpler and avoids unnecessary complexity.
However, there is a more serious problem with the Talmud’s explanation. According to the Talmud, Avraham was disappointed by the absence of travelers. Their absence denied Avraham of the opportunity to extend his hospitality. This is a strange reason for Avraham to become frustrated. True, in the absence of travelers, he could not extend his welcome, but no travelers required his hospitality! In other words, apparently, Avraham was disheartened because he could not practice chesed – kindness. But kindness is a response to a person in need. If one has the opportunity to practice chesed and does not take advantage of the opportunity, then this person has a reason to be disappointed in himself. But it is ridiculous for a person to bemoan the fact that there is no one in need of his help!
Avraham’s concern with the welfare of travelers
This is not the only occasion on which Rashi discusses Avraham’s intense desire to serve travelers. The Torah explains that after the destruction of Sedom and the surrounding cities, Avraham relocated his camp and resettled in Gerrar – located between Kadesh and Shur. Rashi explains that with the destruction of Sedom and the surrounding region, travelers abandoned the routes in the area. Avraham could no longer extend his welcome to travelers. Therefore, he relocated to a more densely populated region. This allowed him to renew his practice of accommodating travelers.  Rabbaynu Ovadia Sforno offers an explanation for Avraham’s relocation to Gerrar, that at first, seems to be an alternative to Rashi’s explanation. He explains that Avraham was dedicated to teaching the truths he had discovered. His mission was to reintroduce Hashem to humanity and to vigorously oppose all forms of idolatry. Avraham could only fulfill this mission in a populated area. The region of Sedom had served as an ideal location for Avraham. It was a relatively densely populated region containing a number of cities. Avraham reached out to the people of the region and taught them and helped them escape the insanity of idolatry. With the destruction of this region, Avraham was forced to relocate in order to continue his mission. He chose Gerrar as his new headquarters. 
However, there is not necessary any disagreement between Rashi and Sforno. Sforno is explaining Avraham’s mission. But Rashi is describing his strategy. Avraham’s mission was to salvage humanity and return it to Hashem. His strategy was to reach people though acts of kindness.
Two paradigms of chesed
The Torah commands us to love our neighbors as we love ourselves.  This seems like an impossible task. But although it is very difficult to achieve this level of empathy, we can strive to be constantly cognizant of the sanctity that is shared by every human being. We are all the work of Hashem. Each of us is created in His form. How do we constantly remind ourselves of this shared sanctity? We achieve this recognition through the acts of loving kindness that we perform for one another. By treating our fellow human beings with sensitivity and kindness – even those with whom we are not familiar and those of whom we are not fond – we remind ourselves that despite all of our deficiencies, we are each the work of Hashem and a reflection of His Divine essence.
This form of chesed is fulfilled through responding to those in pain, who are suffering, or are in need of our assistance. Chesed practiced, as an expression of this paradigm, requires that we respond to those who need our assistance. It may even require that we seek out those in need. But this form of chesed is purely a response to need and in the absence of need, it is not practiced.
There is another paradigm for chesed. Chesed was employed by Avraham as a means of drawing people back to Hashem and away from idolatry. Avraham’s chesed was a concrete expression of his love of Hashem and his desire to serve Him through reaching out to humanity. Avraham did not welcome strangers into his home merely to satisfy their appetite for food. As Sforno explains, Avraham’s mission was to satisfy the spiritual hunger of humanity. Each guest was fed and also drawn into a discussion in which Avraham probed, posed questions, made observations, and gradually penetrated the thinking of the idolater encouraging him to rethink his convictions and abandon his prejudices. Through this process, Avraham drew his guests towards Hashem and away from the folly of idolatry.
Chesed that is an expression of this paradigm – an expression of love of Hashem – is not merely a response to need. Its end is not solely to provide relief. Instead, it treats need as an opportunity to address a more fundamental issue. Need provides the opportunity to reach out to another human being and to be received. It provides an opening into the recipient’s heart and mind. This form of chesed begins with addressing the need identified by the recipient, but this is only its starting point. Its ultimate objective is to reshape the recipient’s thinking, free him from his religious prejudices, and rescue him from the foolishness of idolatry. But this form of chesed does require need in order to gain expression, and in the absence of need, it cannot be performed.
Now, Avraham’s response to the absence of travelers can be understood. The travelers had abandoned the roads to seek shelter from the heat. They did not need Avraham’s assistance. But Avraham was unhappy. Because his assistance was not required, he was deprived of the opportunity to practice chesed and thereby reach out to his fellow human beings. As the sun waxed brightly, Avraham perceived that no one would enter his home on this day and he would lose the opportunity to teach his fellow human being. No new person would be encouraged to abandon idolatry and no one would be drawn into the service of Hashem. Hashem responded to Avraham’s distress by sending him three guests. Avraham seized the opportunity to bring these strangers into his home and into his religious community.
Furthermore, the comments of the Talmud are not longer convoluted. They are an eloquently formulated homiletic teaching. The message communicated is that Avraham’s chesed was not only a response of kindness to those in need. Avraham was unhappy when he could not perform acts of chesed. This frustration – emphasized by the Talmud – indicates the true nature of Avraham’s chesed and identifies the paradigm that it expresses. The message communicated is that Avraham regarded need as an opportunity to reach people. As a result, he bemoaned the absence of this opportunity.
1. Rabbaynu Shlomo ben Yitzchak (Rashi), Commentary on Sefer Beresheit 18:1.
2. Mesechet Baba Metzia, 86b.
3. Yalkut Shimoni on Sefer Beresheit, 18:82.
4. Rabbaynu Shlomo ben Yitzchak (Rashi), Commentary on Sefer Beresheit 20:1.
5. Rabbaynu Ovadia Sforno, Commentary on Sefer Beresheit, 20:1.
6. Sefer VaYikra 19:18