Persevere in prayer…

He taught them only the seven petitions of the Our Father in which all our spiritual and temporal needs are contained, and said nothing further about numerous other kinds of prayers and ceremonies. On the contrary, he urged them not to use many words in their prayers, since our Father in heaven surely knows what we need (Mt 6:7–8). Only one thing did he stress with special emphasis: that we should persevere in prayer.
–Saint John of the Cross (1542-1591)

Prayer and virtues…

Perseverance in prayer cleanses the intellect, illumines it, and fills it with the light of truth. The virtues, led by compassion, give the intellect peace and light. The cleansing of the intellect is not a dialectical, discursive and theoretical activity, but an act of grace through experience and is ethical in every respect. The intellect is purified by fasting, vigils, silence, prayer, and other ascetic practices.
–Saint Isaac of Syria (Seventh Century)