“Va’eschanan el Hashem b’eis ha’hi leimor.” What does the word “leimor” mean in this context? Ramban writes in Shmos 6:20 that the word “leimor” means to articulate clearly, as opposed to “amira m’supekes.” “Vayidaber Hashem el Moshe leimor” means (according to Ramban) that Hashem gave Moshe some message and charged him with the task of articulating it clearly to Bnei Yisrael. That makes sense in the context of a communication from A to B, but here we are not talking about a command that Hashem told Moshe to transmit or a nevuah to relate. Moshe is praying, which is exactly what the word “va’eschanan” on means on its own, without the additional “leimor.” Rashi already tackles this question and writes that the extra word signals that Moshe wanted Hashem to say something in response, but there is another approach as well.
There is another instance of “leimor” in the parsha that the meforshim struggle with: “Anochi omeid bein Hashem u’beineichem ba’eis ha’hi l’hagid lachem es dvar Hashem ki y’yreisem mipnei ha’eish v’lo avisem ba’har leimor.” (6:5) Rashi and Ibn Ezra write that “leimor” is a continuation of “l'hagid lachem es dvar Hashem,” even though there are intervening phrases (Ramban has a different approach). Aside from the problem of the word “leimor” dangling at the end of the sentence, divorced from the preceding phrase, the more fundamental question is why is the word is needed at all. We are dealing with the aseres hadibors, which Hashem communicated directly to Bnei Yisrael. Hashem here doesn’t need to speak to Moshe and impress upon him to articulate the message clearly – Hashem is the one himself who is articulating the message! Rashi again is already bothered by this issue in Parshas Yisro, the first time the aseres hadibros appear and we read, “Vayidaber Elokim… leimor,” and Rashi again explains that the “leimor” indicates a response; Bnei Yisrael responded verbally to each dibra.
My wife’s grandfather, R’ Dov Yehudah Shochet, heard from his rebbe muvhak, R’ Yosef Bloch a different explanation of “leimor” (which the Ohr haChaim anticipates) that is easier for me to try explain using an illustration than by trying to offer a definition. It’s 90+ degrees today, humid, and uncomfortable. Let’s pretend that c”v the air conditioning in your home breaks down. Your wife asks you, “Did you see the ad in the newspaper for air conditioners that are on sale?” The correct answer, even if you saw the ad, is not, “Yes,” full stop. The correct answer is to get in the car and go to the store and buy an air conditioner. But, asks the foolish husband, “She didn’t tell me to buy an air conditioner – she only asked if I saw the ad?” The question indicates that you heard only half the message. The question about the ad was the “vayidaber.” The “leimor” was to go buy the air conditioner. This is similar to what the Ohr haChaim on our parsha (see also O.C. to Shmos 6:12) calls “kollel hamechuvan b’lashon achier.”
“Vatizchak Sarah b’kirbah leimor….” and then she denies it. If she laughed, how could she deny doing it, asks Ramban? If she didn’t, then why is she held accountable?
The answer is (as my wife's grandfather explained) that of course Sarah did not break out in mocking laughter and would never dream of openly questioning the possibility of her having a child. There was no dibur -- she never said it. But “b’kirbah,” inside, she felt something. The Torah translates those emotions into words for us,“leimor,” so that we know what was going on.
When we talk about G-d’s speech, there is no resemblance to what we call speech. “Zachor v’shamor b’dibur echad” – we can’t even imagine what that means. When that experience described by the anthropomorphism “vayidaber Elokim” is translated into speech, “leimor,” the content is the words of aseres hadibros.
Coming back to the first pasuk in our parsha: tefilah has to come from within, otherwise the words have no meaning and don't carry any weight. “Va’eschanan el Hashem,” was a personal meditation. If we translate, "leimor", those thoughts and emotions into speech, the words that followed are the result. (This last point is from the Ohr haChaim)