Fire discourse
From the Samyutta Nikaya (a):
Gautama: At such times, monks, as the mind is sluggish, that is the wrong time to cultivate the enlightenment-factor of tranquility, the enlightenment-factor of concentration, the enlightenment-factor of equanimity.
What is the reason? A sluggish mind is hard to arouse by these factors.
Suppose a man wants to make a small fire blaze. If he heaps wet grass, wet cow-dung and wet sticks on it, if he exposes it to wind and rain and sprinkles it with dust, can he make that small fire blaze?
Anonymous bhikku: No indeed, Lord.
Gautama: Just so, when the mind is sluggish it is the wrong time to cultivate the enlightenment-factors of tranquility, concentration and equanimity, because a sluggish mind is hard to arouse through these factors.
But, monks, when the mind is sluggish, that is the right time to cultivate the enlightenment-factor of investigation-of-states, the enlightenment-factor of energy, the enlightenment-factor of rapture.
What is the reason? A sluggish mind is easy to arouse by these factors.
Suppose a man wants to make a small fire blaze. If he heaps dry grass, dry cow-dung and dry sticks on it, blows on it with his mouth, and does not sprinkle it with dust, can he make that fire blaze?
Anonymous bhikku: Yes indeed, Lord.
Gautama: ... a sluggish mind is easy to arouse through these factors.
Monks, when the mind is agitated, that is the wrong time to cultivate the enlightenment-factors of investigation-of-states, of energy, of rapture.
Why? An agitated mind is hard to calm through these factors.
Suppose a man wants to put a big fire out. If he heaps dry cow-dung and dry sticks on it, blow on it with his mouth, and does not sprinkle it with dust, can he put that fire out?
Anonymous bhikku: No indeed, Lord.
Gautama: ... an agitated mind is not easy to calm through these factors.
When the mind is agitated, that is the right time to cultivate the enlightenment-factors of tranquility, concentration, equanimity.
Why? Because an agitated mind is easy to calm through these factors.
Suppose a man wants to put out a big fire. If he heaps wet grass, wet cow-dung, wet sticks on it and if he exposes it to wind and rain, if he sprinkles it with dust, can he put that big fire out?
Anonymous bhikku: Yes indeed, Lord.
Gautama: Just so, monks, when the mind is agitated, that is the right time to cultivate the enlightenment-factors of tranquility, concentration, equanimity. An agitated mind is easy to calm through these factors.
But as for mindfulness, monks, I declare that it is always useful.