The Buddha discovered [a] twofold division of thought in the period prior to his Enlightenment... While he was striving for deliverance, meditating in the forest, he found that his thoughts could be distributed into two different classes.
In one he put thoughts of desire, ill will, and harmfulness, in the other thoughts of renunciation, good will, and harmlessness.
Whenever he noticed thoughts of the first kind arise in him, he understood that those thoughts lead to harm for oneself and others, obstruct wisdom, and lead away from Nibbana. Reflecting in this way he expelled such thoughts from his mind and brought them to an end.
But whenever thoughts of the second kind arose, he understood those thoughts to be beneficial, conducive to the growth of wisdom, aids to the attainment of Nibbana. Thus he strengthened those thoughts and brought them to completion.
Bhikkhu Bodhi on right intention
If you consider this awhile and begin to work with it, there may first be frustration if you are putting much effort into expelling and strengthening thoughts. Please avoid this trap. Seeing clearly, seeing the two kinds of thought occuring is transformative in itself. In time the mind will naturally turn toward what is wholesome. This wholesome turning cannot happen if we are blind to what is occuring in the mind (The buddhist meaning of ignorance here is more like foggy or uninformed).
