Prayer to prepare your heart based on Psalm 46:

Lord God, our refuge and strength,
when the restless powers of this world
and the waters of hell rise up against your holy city,
watch over it and keep it safe.
By the river that flows from the throne of the Lamb,
purify us, your new Jerusalem,
as your chosen dwelling,
for You are with us, our stronghold now and forever. AMEN.