1) RECEIVING MONEY FOR THE MITZVAH OF "BIKUR CHOLIM"
OPINIONS: The Gemara teaches that even in places where people who visit the sick charge money for their services, the visitor should demand payment only when he sits down during the visit. If he remains standing, he should not take any payment.
Why is it improper to take payment for standing up while visiting the sick?
(a) The ROSH (printed on 38b) writes that one should not take payment for visiting the sick because doing so belittles the Mitzvah. Taking payment for sitting is permitted because he takes money for the extra time he spends with the sick person (and thereby must take off from his work) and not for the fulfillment of the obligatory element of the Mitzvah itself.
(b) TOSFOS writes that since it is a Mitzvah to visit the sick, one should do so for free. This is based on the Gemara earlier (37a) which says that one may not take a wage for teaching Torah. That Halachah is not limited to teaching Torah, but it applies to the performance of any Mitzvah (see Kesuvos 105a).
According to Tosfos, why is one permitted to take payment for sitting down while he visits the sick? Tosfos apparently agrees with the Rosh that one may take money for the extra time he spends with the sick person and not for the actual Mitzvah.
The Rosh may understand that the restriction against taking a wage for performing a Mitzvah applies only to Mitzvos explicitly written in the Torah. Therefore, the Rosh gives a different reason than the one Tosfos gives for why one should not take payment for visiting the sick.

39b----------------------------------------39b

2) THE SOURCE FOR THE MITZVAH OF "BIKUR CHOLIM"
QUESTION: Reish Lakish says that the Torah alludes to the Mitzvah of Bikur Cholim in the verse in Parshas Korach, "If these die like the death of all man, and the fate of all man is visited upon them..." (Bamidbar 16:29). The Gemara in Bava Metzia (30b) derives the Mitzvah of Bikur Cholim from the verse in Parshas Yisro, "You shall inform them of the path in which they should go..." (Shemos 18:20). The Gemara in Sotah (14a) derives the Mitzvah of Bikur Cholim from the verse in Parshas Re'eh, "After Hash-m your G-d you shall follow..." (Devarim 13:5), the command to emulate the attributes of Hash-m; just as Hash-m visits the sick, so must we.
Why are there three different sources in the Torah for the Mitzvah of Bikur Cholim?
ANSWERS:
(a) The ROSH writes that the Gemara here seeks a more explicit reference to the Mitzvah of Bikur Cholim than the verses cited in Bava Metzia and Sotah. It quotes the verse in Parshas Korach which is more explicit than the verse in Parshas Yisro and the verse in Parshas Re'eh.
(b) The RAMBAM understands that Bikur Cholim is actually part of two different Mitzvos. In SEFER HA'MITZVOS (Mitzvah 8) the Rambam writes that there is a Mitzvah to emulate Hash-m's attributes. He writes that this Mitzvah is derived from the verse in Parshas Re'eh cited by the Gemara in Sotah. It is also learned from the verse in Parshas Yisro cited by the Gemara in Bava Metzia. This Mitzvah -- to emulate the ways of Hash-m -- is recorded by the Rambam in the Mishneh Torah in Hilchos De'os (1:5-6). This is the first general Mitzvah which includes the Mitzvah of Bikur Cholim.
Later in Sefer ha'Mitzvos (Mitzvah 206), the Rambam writes that there is a Mitzvah for every Jew to love every other Jew and to wish for his fellow man everything that he would want for himself. In the Mishneh Torah (Hilchos Avel 14:1), the Rambam writes that all of the Mitzvos of Gemilus Chasadim (including visiting the sick) are included in the Mitzvah of loving one's fellow man. (The SEFER HA'CHINUCH also counts these two Mitzvos as two separate Mitzvos (#243 and #611).)
The Rambam apparently understands that the Gemara here seeks a source in the Torah that the Mitzvah of Bikur Cholim is part of the Mitzvah of loving one's fellow man. The Gemara in Sotah and in Bava Metzia provide sources that Bikur Cholim is part of the Mitzvah of emulating the ways of Hash-m.
There is a basic difference between the Mitzvah of loving one's fellow man and the Mitzvah of emulating the ways of Hash-m. The Mitzvah of loving one's fellow man is a Mitzvah "Bein Adam la'Chaveiro," to care for the needs of one's fellow man. The Mitzvah of emulating the ways of Hash-m is a Mitzvah "Bein Adam la'Makom," to bring oneself closer to Hash-m and His ways. The Sefer ha'Chinuch writes that the purpose behind the Mitzvah of loving others is that there should be peace among people. The purpose of emulating Hash-m is that people live in accordance with Hash-m's will. The Mitzvah of Bikur Cholim incorporates both types of Mitzvah.
The Gemara in Bava Metzia asks why a verse is needed to teach that there is a Mitzvah to visit the sick. The Gemara answers that although it is known that one who visits the sick receives part of the sickness if he shares the same Mazal as the sick person (see Insights to Nedarim 40:1), he nevertheless fulfills a Mitzvah by doing so. This can be explained based on the above distinction: if one is required to visit the sick only as a Mitzvah Bein Adam la'Chaveiro, he is not required to endure any personal loss or suffering to do the Mitzvah (unless one thereby is able to save his friend's life). By finding a source that Bikur Cholim is also part of the Mitzvah of emulating Hash-m's ways and is a Mitzvah Bein Adam la'Makom, the Gemara teaches that one is required to fulfill the Mitzvah even if it will cause him personal discomfort.
3) THE STATUS OF THE MITZVAH OF "BIKUR CHOLIM"
QUESTION: Reish Lakish says that the Torah alludes to the Mitzvah of Bikur Cholim in the verse, "If these die like the death of all man, and the fate of all man is visited upon them..." (Bamidbar 16:29). The Gemara in Bava Metzia (30b) and Sotah (14a) cites two other verses that allude to the Mitzvah of Bikur Cholim (see previous Insight).
Do these sources imply that the Mitzvah of Bikur Cholim is a Mitzvah d'Oraisa?
(a) The BEHAG and YERE'IM count the Mitzvah of Bikur Cholim as one of the 613 Mitzvos d'Oraisa.
(b) The RAMBAM and RAMBAN in Sefer ha'Mitzvos (Shoresh Rishon and Sheni) maintain that Bikur Cholim is not an independent Mitzvah but is included in another, more general Mitzvah.
The RAMBAM (Hilchos Evel 14:5) writes that Bikur Cholim is a Mitzvah "mi'Divreihem," which implies that it is a Mitzvah d'Rabanan. However, he continues to list other Mitzvos (such as Nichum Aveilim) and concludes that although these Mitzvos are "mi'Divreihem" they are part of the Mitzvah d'Oraisa of "v'Ahavta l'Re'acha Kamocha," loving one's fellow man like oneself.
The Rambam seems to contradict himself. If Bikur Cholim is part of the Mitzvah d'Oraisa of loving one's fellow man, why does he say that it is a Mitzvah d'Rabanan?
The KIRYAS SEFER answers that the Rambam understands that there is a general Mitzvah to love one's fellow man, but the specific ways of fulfilling it were enacted by the Rabanan. An example of this concept is the Halachah that one who visits the sick but does not pray for the recovery of the sick person does not fulfill the Mitzvah. While one fulfills the Mitzvah d'Oraisa of loving his friend with any act that he does for his friend's well-being, the Rabanan required that one visit the sick in a certain manner. If he does not pray for the sick, he has not fulfilled this requirement.
(The fact that the specific forms of the Mitzvah are only mid'Rabanan may be relevant to the law of "ha'Osek b'Mitzvah Patur Min ha'Mitzvah"; see BI'UR HALACHAH, end of OC 72.)