St. Isaac the Syrian: Thirst for Jesus

 Thirst for Jesus, that He may make you drunk with His love. Close your eyes to the delights of this life, that God my deem you worthy to have His peace reigning in your heart. Abstain from what your eyes behold that you may be accounted worthy of the spiritual joy.

+St. Isaac the Syrian, from Ascetic Homilies, homily 3.

St. Isaac the Syrian: Humility in prayer

 When the humble-minded man approaches prayer or becomes worthy of it, he still does not dare to petition God or ask for anything. He does not yet know for what he should pray; all his thoughts are silent, awaiting only the mercy and the will of the God Whom he worships. His face is bowed to the earth, and the inner eye of his heart is raised to the exalted gates of the Holy of Holies. There is He Whose dominion is the darkness that dims the eyes of the Seraphim, Whose goodness inspires countless legions of angles to worship in complete silence. The boldness of this man only extends to the follow words that he dares utter in prayer: "O Lord, let it be with me according to Thy will." (cf. Luke 1:38).

+ St. Isaac the Syrian, from Ascetic Homilies, homily 49.

St. Isaac the Syrian: On the measure of our thoughts

 You may comprehend the measure of your way of life from that which arises in your mind with regard to what is muses on in its thoughts; for which things your nature effortlessly longs, what stirrings are aroused continually, and which are caused by an accidental circumstance; whether your mind has any perception at all of incorporeal thoughts; or whether all its motions are of a material sort; and whether the mind's material quality is something passionate, or only that the thoughts are imprints of the physical aspect of a man's virtuous labor: for the mind involuntarily muses upon the things wherewith it performs the virtues. From these things [last mentioned] the mind, in a wholesome manner, receives the cause of fervor and the gathering of its deliberations, for because of its lack of training the mind, with a good intention, prefers to labor in a corporeal manner, though it does not do so passionately. Observe also whether your mind remains unaffected by hidden confrontations with the imprints of thoughts because of a mightier ardor for the Divine, which is wont to cut off vain recollections.

+St. Isaac the Syrian, from Ascetic Homilies, homily 2.

St. Isaac the Syrian: On devotion to learning from the Scriptures

 Nothing can so banish licentious habits from the soul and restrain memories which disturb and stir up troubling flames in the body as can avid devotion to the love of learning and searching investigation into the meanings of the passages of Scripture.

When the impulses of the soul plunge into the pleasure which comes from the wisdom stored in the words of Scripture, vigorously drawing understanding from it, a person will leave his body behind. Such a one will forget the world and all that is in it and will cancel from the soul all the memories which stir up images of the material world. Often the soul in wonder desists in its reflection from the use of habitual thoughts which come naturally to it, in the presence of the novelties which come to it from the sea of the Scripture's mysteries.

+St. Isaac the Syrian, from On Ascetical Life, First Discourse #16-17.

St. Isaac the Syrian: On thankfulness to God

The thanksgiving of the recipient incites the giver to give gifts greater than the first. He that returns no thanks in small matters is a dissembler and dishonest in greater ones also. If a man is ill and recognizes his ailment, his healing will be easy. If he confesses his pain, he draws nigh its cure. The pangs of the unyielding heart will be multiplied, and the patient who resists his physician amplified his torment. There is no unpardonable sin, save the unrepented one. Nor does any gift remain without addition, save that which is received without thanksgiving. The fool's portion is small in his eyes.
+St. Isaac the Syrian, from The Ascetical Homilies, Homily 2 On thankfulness to God, in which there are also essential elementary lessons.

St. Isaac the Syrian: Purity of mind

Of what does purity of mind consist? The "pure of mind" is not a person who does not know evil things, surely such a one would be an animal. Nor doe we call "pure of mind" those whom nature has placed in a condition of innocence, (cf. Matt 19:12) unless we require that persons do not even belong to the order of created beings. (Job 4:17-18; 15:14-16) But purity of mind is captivation by divine things, which comes about after the practice of many virtues.
+St. Isaac the Syrian, from On Ascetical Life, Third Discourse