This verse comes from Yirmiyahu (Jeremiah) 31:33 and is also echoed in Yeshayahu (Isaiah) 11:9.

This prophecy refers to the time of the Messianic era when the knowledge of Hashem will be so widespread and accessible that there will be no need for one person to teach another about Hashem. Everyone, from the smallest to the greatest, will naturally possess a deep understanding of Hashem's presence and truth. The phrase "the earth will be filled with the knowledge of Hashem" signifies a time of universal recognition and connection to the Divine, bringing peace and spiritual clarity to the world.