The answer is: In a burning bush

Exo 3:2

The encounter between Moses and the angel of the Lord in the form of a burning bush is one of the most iconic moments in the Biblical narrative. Adorned with great symbolism, the burning bush represents God's divine presence and His holiness. Despite being engulfed in flames, the bush miraculously does not burn up. This is a profound lesson in resilience and divine intervention. In this moment, Moses is reminded that while the hardships of his task might seem overwhelming, God equips the humble with strength, just as the bush withstands the fire.

This aspect of God's communication shows a pattern throughout Scripture where the extraordinary interrupts the ordinary, like God later manifesting in clouds and pillars of fire during Exodus. Fun trivia: The location, Mount Horeb, is also referred to as "the mountain of God" and is believed by many to be the same as Sinai, where Moses would receive the Ten Commandments. “Horeb” literally translates to "desolate," yet in desolation, transformation occurs when Moses receives his calling.

Additionally, back in Genesis, God also appears in forms of dreams and visions—similar symbolic actions that demonstrate God’s omnipresence in guiding humanity. It’s an incredible reminder of how divine communications come when least expected, flipping the mundane into the miraculous. Moses' initial response showcases a mix of fear and intrigue, a natural human reaction when confronted with the divine. This moment sets the stage for a colossal journey, where one man's reluctance sparks a movement of freedom for an entire people.