The conditions of Samadhi - Samyutta Nikaya 46.53

The Buddha described the preparation made for fire, saying,

Suppose you want to make a small fire into a large fire: if you put wet fuel on it, expose it to wind and rain, or sprinkle it with dust, will that make the small fire grow? Just so, the mind requires proper fuel and conditions for enlightenment: tranquility, peace and equanimity. These three conditions can wake a sluggish mind. How are these conditions achieved? Through curiosity, will and energetic exertion, and playful love or friendship.

And what are the conditions for tranquility, curiosity, will and energetic exertion, and playful love or friendship? These are the conditions of enlightenment (bojjihanga - limbs of enlightenment, so-called because they lead to enlightenment): mindfulness (sati-sambojjangha), understanding of mental and physical natures (dhamma-vicaya-s, connoting "science"), exertion or energy (viriya-s), playful love or friendship (piiti-s, different than Sukha - happiness, contentment), tranquility (passaddhi-s), peace (samaadhi-s), equanimity (upekkhaa-s).

Suppose you want to start a fire: if you have only wet fuel, if it is windy and rainy, if you sprinkle it with dust, will you be able to start a fire? Those are the wrong conditions to start a fire. Just so, when a mind is agitated it is the wrong time to wake it to enlightenment. A new fire is easily extinguished, but a large fire is not. It is difficult to wake, it is more difficult to wake to enlightenment, but it is even more difficult to extinguish the flame of enlightenment.

And what is the condition for extinguishing agitation, to permit sluggishness to be roused into wakefulness? Mindfulness. Mindfulness is always useful, in every circumstance, whereas the other conditions are only sometimes appropriate.

This fire, producing the light of wakefulness, of Bodhi, is Agni