Genesis 38:17

And he said, I will send thee a kid of the goats from the flock. And she said, If thou wilt give me a pledge until thou shalt have sent.

עד שלחך. The reason why we have the “weak” mode, i.e. the conjugation kal instead of the transitive conjugation hiphil, is to indicate that Yehudah would send a messenger to deliver the kid to Tamar. We find the use of the conjugation kal in connection with the sending of gifts especially, as for instance in 32,19 where Yaakov had instructed his messengers to Esau to describe the gift in such terms. (מנחה היא שלוחה) We find it again in verse 23 of our chapter where Yehudah says הנה שלחתי הגדי הזה, “here, I have sent this kid, etc.”

אם תתן ערבון, if you are prepared to give me such tokens I am willing to sleep with you as you requested.

ותאמר אם תתן לי ערבון, “she said: ‘if you will give me a pledge;’” some commentators claim that Yehudah did not sleep with Tamar until after he had given her a token to serve as a marriage betrothal. They interpret her question above as her asking for such a token. It was meant to mean: “what kind of token of your intention to wed me are you going to give me?” Yehudah’s answer was that he would send her a young goat. Thereupon she asked for a guarantee that he would indeed send that goat. By insisting that he would give her his signet ring she meant that this would be her wedding ring. According to Rabbi Moshe, this whole interpretation is difficult to accept as the handing over of such a token requires the presence and confirmation by two witnesses in good standing as spelled out in the Talmud, tractate Kiddushin folio 65. Some people claim that an important person such as Yehudah would never travel except in the company of at least two people who could qualify as witnesses, just as a Torah scholar in our time does not travel alone and that therefore the betrothal of Tamar had been duly witnessed. If you were to counter that the betrothal was still invalid as she had never received the promised goat from him, and the Talmud in Kiddushin folio 8 states that even if the suitor gave the bride a token worth a p’rutah (smallest copper coin) as a pledge to cover the remainder, such a betrothal is not legally valid. We would therefore have to say that he gave her his signet ring not as a pledge, but as an outright gift at that time. After having done so, he told her that when he would send her the goat he expected her to return his ring. This is how, in my opinion, the author of the above interpretation must have meant it.