Cast out every sinful thought…

Since prayer is an association of the mind with God, then in what state must the mind possibly be, in order to be able, without turning elsewhere, to approach its Lord and converse with Him without the mediation of something else?  If Moses in his attempt to approach the burning bush was hindered until he had removed the sandals from his feet, then shouldn’t you who desires to see God and converse with Him, remove and cast out of you every sinful thought?
–Saint Nilus of Sinai (d. 430)

In knowing God…

Let us occupy ourselves entirely in knowing God. The more we know Him, the more we will desire to know Him. As love increases with knowledge, the more we know God, the more we will truly love Him. We will learn to love Him equally in times of distress or in times of great joy.
–Brother Lawrence (1614-1691)

Laying aside some devotion…

It is, however, necessary to put our whole trust in God, laying aside all other cares, and even some particular forms of devotion, though very good in themselves, yet such as one often engages in unreasonably: because those devotions are only means to attain to the end; so when by this exercise of the presence of God we are with Him who is our end, it is then useless to return to the means; but we may continue with Him our commerce of love, persevering in His holy presence: one while by an act of praise, of adoration, or of desire; one while by an act of resignation, or thanksgiving; and in all the manner which our spirit can invent.
–Brother Lawrence (1614-1691)