It is not uncommon in grammar to find an understood, but not stated, subject or object. Often this comes in the case of a command, such as “sit.” It is reasonably assumed that the person being addressed is the one who should sit. Similarly, if one were to say, “He drove off the cliff,” most people would think of a vehicle being driven. In fact, that would be the assumption unless a more specific object was supplied. You don’t expect the object of that sentence to be a herd of swine unless it specifically says, “He drove the herd of swine off the cliff.” In most modern printings of the King James Version and some other Bibles, certain words are in italics, indicating that they were supplied by the translators as being understood.
One example that has led to a traditional reading can be found in the plagues of Egypt. Exodus 8:21-29 relates the plague commonly called the plague of flies. You can’t even blame King James for this, because as early as Jerome’s Vulgate the word flies was supplied. What Moses actually said was that he would send swarms on Egypt. Some rabbis think this was wild animals, even though you don’t often think of them in terms of swarms. Others have said it was mosquitos, which probably makes more sense than either of the others. Nevertheless, the object of swarms is supplied by the translators.
At this time of year there is another instance of a supplied object. Rosh HaShanah will begin on the evening of September 18 in 2020. On that day it is required that the Jewish people hear at least 30 blasts on the shofar, and some authorities require one hundred blasts. Most Jews would be surprised to learn that the passage in Leviticus describing the holiday does not specifically mention trumpets or shofarim.
Speak unto the children of Israel, saying, In the seventh month, in the first day of the month, shall ye have a sabbath, a memorial of blowing, an holy convocation. (Lev 23:24)
Most translations supply the “of trumpets” after blowing. It is a reasonable assumption. When the requirements of the holiday are repeated in Numbers, the statement is more specific. “It is a day of alarm to you.” (Num 29:1) The specific method of sounding an alarm for the Jewish people was the blowing of the shofar. Even though “trumpets” is still an assumed word in Numbers, it is a much more specific one than in Leviticus.
It is reasonable to ask what else it could be that is to be blown? One has no control over the blowing of the wind. What would be the point of blowing bubbles, assuming anyone did that so long ago? Blowing trumpets or blowing an alarm are the reasonable assumed objects in the passage.
But why is this day singled out for blowing? There are twelve or thirteen months. Why would the head of this one be chosen for a celebration? Probably it is because of the events ten days later.
The seventh month is noted for three holidays: Trumpets, Atonement, and Booths. The head of the month is characterized by an alarm, because the Day of Atonement is coming. The Jewish people would need to prepare their minds and actions for that day. It is a responsibility to blow the alarm.
But if the watchman see the sword come, and blow not the trumpet, and the people be not warned; if the sword come, and take any person from among them, he is taken away in his iniquity; but his blood will I require at the watchman's hand. (Ezek 33:6)