The Ark symbolizes the power to preserve all things and to ensure their rebirth, on both material and spiritual planes. It symbolizes salvation.
The Ark saved Noah and his family from drowning in the Biblical flood. It can be seen as both the instrument of God's justice and punishment; the ark represents God’s shelter for the faith and the rebirth when the necessary conditions were created again.
In medieval mysticism, it is often symbolic of the heart (or of the mind, or of thought).