Genesis 38:24

And it was at the time of three months, that she was known to be with child: and it was told to Jehuda, saying Tamar thy daughter--in--law hath committed fornication and, behold, she is with child by fornication. And Jehuda said, Is she not the daughter of a priest. Let her be brought forth and burned.

AND JUDAH SAID: BRING HER FORTH, AND LET HER BE BURNT! Ephraim Makshoah,); (b) he was a scholar famous for his great ability in debate (kasheh). See Commentaries to Bereshith Rabbah 84:11. a disciple of Rabbi Meir, said in the name of Rabbi Meir: “Tamar was the daughter of Shem who was a priest. They therefore sentenced her to be burnt.” Rashi quoted this Midrash but did not explain it. And I do not know this law, for a priest’s daughter is not liable to be burned except for harlotry in conjunction with a binding relation to a husband, either espoused or married, as is explained in the Gemara in Tractate Sanhedrin. However, a priest’s daughter who is waiting to be married by a brother-in-law is not at all liable to death for harlotry. Whether she is an Israelite’s daughter or a priest’s daughter, her punishment is only that of having violated a simple negative precept. And should you say that marrying a childless brother’s wife was customary among the Sons of Noah, and that she was regarded by them as having the status of a married woman, and that their prohibitions were punishable by death, it would not be correct. The Rabbis say in Bereshith Rabbah that Judah was the one who first inaugurated the observance of the commandment that a brother marry a childless brother’s widow. And again, in the Gemara in Tractate Sanhedrin, it is made clear that a childless brother’s widow of the Sons of Noah is not at all liable to any punishment for harlotry.
It appears to me that since Judah was a chief, an officer, and a ruler of the land, his daughter-in-law who committed harlotry against him was not judged by the same law as other people, but as one who degraded royalty. It is for this reason that it is written, And Judah said: Bring her forth, and let her be burnt, for the people came before him to do unto her in accordance with his command, and he declared her guilty of a capital crime because of the superior rank of royalty. Thus he judged her as if she had profaned her father in respect of his priesthood, but this was not the judgment meted out to commoners.
In line with the literal interpretation of Scripture, it is possible that their law was similar to that which is presently customary in some of the countries of Spain, i.e., that a married woman who commits a faithless act is turned over to her husband who decrees death or life for her, as he wishes. Now Tamar was designated for his son Shelah, and in the eyes of their laws she was considered as a married woman.

זנתה תמר כלתך, if you were to ask why Yehudah would believe such accusations which would be hard to prove, the informant added that the signs of her pregnancy spoke for themselves as proof of the accusation being justified.

ותשרף, according to the plain meaning of the text this was the standard penalty for a widow of Tamar’s status who had engaged in illicit sex.

וגם הנה הרה, she did not even bother to hide her condition which reflects negatively on you. This is similar to a statement by our sages in Yevamot 35 “when a woman had illicit sex she engages in all kinds of bodily convulsions to avoid becoming pregnant and thereby revealing her shame and that of her husband or lover.”

ויהי כמשלש חדשים, after, or at the end of. The letter כ is used to describe a quantity, a measure, as in Samuel I 14,14 כעשרים איש, “approximately 20 people.” There are numerous similar examples in Scripture for the use of the prefix כ in that sense. In Bereshit Rabbah 85,10 Sumchus quotes Rabbi Meir as having said that this verse is the source of the statement that we cannot tell by looking at her that a woman is pregnant until 3 months after she conceived. Rabbi Hunna, quoting Rabbi Yosseph, added that what is meant is not that until the end of the third month of pregnancy no signs are visible. The pregnant woman herself can perceive signs after as little as 2 weeks, but outsiders cannot. [I amended the text of Rabbi Hunna’s comment in order to make it understandable. Ed.]

הוציאוה, to the site reserved for such executions by fire.

ותשרף, for in accordance with the local practice a widow awaiting to be wed to her brother-in-law was subject to the same rules of adultery as a regularly married woman, i.e. death by burning. At the same time, she was not out of bounds to her father-in-law if he wanted to marry her in order to have seed from his deceased son. Both other sons of the surviving father and the father himself were close relatives of the deceased, after all. The surviving brother of the deceased had the first claim on such a widow, but Tamar, under the circumstances had been forced to become the wife of Yehudah seeing that Shelah had been denied her.

זנתה תמר כלתך, “your daughter-in-law Tamar has committed an act of adultery.” Why did the informant have to add that Tamar had also become pregnant as a result of her act of adultery? Perhaps we can answer that in that era when acts of adultery did not result in the woman becoming pregnant as a result, no legal proceedings were instituted against her. Alternately, proceedings used to be instituted after such a woman had committed adulterous acts with more than one individual.