Halakhah for Exodus 34:19

That is that He commanded us to count the years and the sabbatical cycles until the Jubilee year, once the land has been conquered and we have subdued it. And this commandment - meaning the counting of the years of the sabbatical cycle is given over to the Great Court, meaning the Great Sanhedrin. For they are the ones that count each year of the fifty years, just like each and every one of us counts the days of the omer. And that is His, may He be exalted, saying, "And you shall count off seven weeks of years" (Leviticus 25:8). And the language of the [Sifra] (Sifra, Behar, Section 2:1) is, "I might think that one counts seven sabbatical years, one after the other, and then have the Jubilee. [Hence] we learn to say, 'seven years, seven times.' [This was not] until both verses were stated; if not, we would not have understood [the law.]" That is to say that the nature of this commandment's performance is only attained with two verses - and that is that he counts the years individually and counts the cycles with them, seven times. And once it says that this matter is only attained from two verses, it indicates that they are perforce one commandment. For had they been two commandments - meaning the counting of the sabbatical cycles and the counting of the years - they would not have said, "[This was not] until both verses were said." For we always learn two commandments from two verses; and likewise always learn every singular commandment from one verse. However, it is said that this is not at all [understood] until two verses were said for this one commandment - the knowledge of which would be incomplete without the two verses. This is like [the commandment of] the firstborn animal that comes from the verse, "All that opens the womb is Mine" (Exodus 34:19). However this alone would indicate that the firstborn would be the Lord's, whether male or female. But another verse comes - "the males are the Lord's" (Exodus 13:12). However that verse by itself would indicate that all the males are the Lord's - whether they are a firstborn or [not]. Rather the content of the commandment comes from the two verses, which is that it is only a firstborn male, like they explained in the Mekhilta. (See Parashat Behar; Mishneh Torah, Sabbatical Year and the Jubilee 10.)