Rashi on Leviticus 19:10/רש"י על ויקרא י״ט:י׳

1לא תעולל AND THOU SHALT NOT GLEAN [THY VINE YARD] — (עלל is a verb connected with the noun עולל "young, tender, not developed"; cf. Samuel 15:3: עולל ויונק) thus לא תעולל means, thou shalt not take the tender grapes of it. They can be recognized as such from the description given in Mishna Peah 7:4 (cf. also Sifra, Kedoshim, Chapter 3 3) where it is stated: What are עוללות? Clusters which have neither כתף, “arms" nor נטף, "drippings".

2ופרט כרמך [NEITHER SHALT THOU COLLECT] THE FALLEN GRAPES OF THY VINE YARD — i. e. the single berries of the grapes which fall to the ground during the grape gathering.

3אני ה'‏‎‎‎‎‎ אלהיכם I AM THE LORD YOUR GOD — the Judge Who am certain to punish if necessary and Who for the neglect of these duties will exact from you nothing less than your souls, as it is said (Proverbs 22:22, 23) "Rob not the poor… for the Lord will plead their cause, [and spoil the soul of those that spoiled them]" (Sifra, Kedoshim, Chapter 3 7).