Let Nothing Disturb You

I am not entirely sure what the name of this particular passage is, but I came across it the other day and loved it:

Let nothing disturb you,
Let nothing frighten you.
All things are passing;
God never changes.
Patience overcomes all things.
He who possesses God
lacks nothing.
God alone is sufficient.
-St Teresa of Avila, 1515 - 1582