I spake unto you at that time. The somewhat indefinite phrase, "at that time" (comp. Genesis 38:1), does not refer to the time after the people departed from Horeb, but to the time generally when they were in that region (see Exodus 18:5, Exodus 18:13).
"The imperfect ( וָאֹמַד, I spake), with vaw rel. expresses the order of thought and not of time" (Keil). It is not mentioned in Exodus that Moses spake to the people, as here stated, but what Jethro said to him to this effect is recorded; and as Moses proceeded to put in execution what his father-in-law advised, it is probable that in doing so he told the people what he proposed to do, with his reasons for so doing, and obtained their assent, as here mentioned.