Rashi on Exodus 19:13/רש"י על שמות י״ט:י״ג

1ירה יירה HE SHALL SURELY BE CAST DOWN — From this we derive the law regarding those who are sentenced to be stoned that they have to be thrown down from the place of stoning, which was a spot of the height of twice a man’s stature (Sanhedrin 45a).

2יירה means HE SHALL BE THROWN BELOW to the ground, the word being similar to, (Exodus 15:4) “He hath cast down (ירה) into the sea”.

3במשך היבל WHEN THE RAM’S HORN SOUNDETH LONG — when the ram’s horn draws out a long sound that is a sign of the departure of the Shechina and that the Divine voice is about to cease, and as soon as “I” shall depart they shall be permitted to ascend [i. e. המה יעלו בהר is not obligatory, signifying, “they shall go up”, but it is permissive] (Mekhilta).

4היבל — This denotes a ram’s horn, for so do they term, a ram in Arabia — יובלא (corresponding to the Hebrew יובל) (Rosh Hashanah 26a). The horn used here was that of Isaac’s ram (Pirkei DeRabbi Eliezer 31).