This verse from 2 Esdras 6:13 is part of a vision experienced by the seer Ezra (also known as Salathiel in some translations). Let's break down the meaning:

"So he answered and said to me...": This refers to an angel or divine messenger who is communicating with Ezra. Ezra is likely in a state of distress or contemplation, seeking answers to profound questions about God's plan and the suffering of his people.

"...Stand up upon your feet...": This command signifies several things:

Readiness and Attention: It's an instruction to be alert and prepared to receive an important message. Standing indicates respect and attentiveness.
Empowerment: It could suggest that Ezra is feeling weak or discouraged. Being told to stand up implies a regaining of strength and dignity. He is being empowered to hear the truth.
A Change in Perspective: Standing can also be symbolic of a shift in perspective, from a humbled or defeated position to one of greater understanding.

"...and you shall hear a mighty sounding voice;": This promises that Ezra will receive a significant revelation. The "mighty sounding voice" suggests:

Authority and Power: The voice is not ordinary; it carries the weight of divine authority.
Importance of the Message: The message that follows is of great importance and impact. It's not a casual conversation but a profound communication.
Resonance and Influence: The voice suggests that the message will resonate deeply with Ezra and likely influence his understanding of the world and God's plan.

In essence, the verse is a moment of preparation and promise. Ezra is being instructed to ready himself, both physically and mentally, to receive a powerful and important message from a divine source. It sets the stage for the revelation that follows, suggesting that it will be transformative and impactful for Ezra. The voice he will hear will be one of authority and will provide answers to the questions he has been grappling with.