The kingdom of God is within us when God reigns in us, when the soul in its depths confesses God as its master, and is obedient to Him in all its powers. Then God acts within it as master ‘both to will and to do of his good pleasure’ (Phil. ii. 13). This reign begins as soon as we resolve to serve God in our Lord Jesus Christ, by the grace of the Holy Spirit. Then the Christian hands over to God his consciousness and freedom, which comprises the essential substance of our human life, and God accepts the sacrifice; and in this way the alliance of man with God and God with man is achieved, and the covenant with God, which was severed by the fall and continues to be severed by our willful sins, is re-established. This inner alliance is sealed, confirmed, and given the strength to maintain itself by the power of grace in the divine sacrament of baptism, and for those who have fallen after baptism, in the sacrament of repentance: and afterwards it is constantly strengthened by holy communion. All Christians live thus; and consequently they all bear the kingdom of God within themselves, that is to say they obey God as King and are ruled by God as King.
This reversal of thoughts is the strongest means, not only for repelling accidental critical thoughts, but also for completely freeing yourself of this vice…
If we desire to acquire faith the foundation of all blessings, the door to God's mysteries, unflagging defeat of our enemies, the most necessary of all the virtues, the wings of prayer and the dwelling of God within the soul--we must endure every trial imposed by our enemies and by our many and various thoughts... if we forcibly triumph over the trials and temptations that befall us, it will not be we who are victorious, but Christ, Who is present in us through faith.
Concerning fasting, do not grieve, as I have said to you before: God does not demand of anyone labors beyond his strength. And indeed, what is fasting if not a punishment of the body in order to humble a healthy body and make it infirm for passions, according to the word of the Apostle: 'When I am weak, then am I strong' (II Corinthians 12:10).
Nothing so abets our secret destruction as conceit and self-satisfaction, or so cuts us off from God and provokes our chastisement at the hands of other men as grumbling, or so disposes us to sin as a disorderly life and talkativeness.
Not every man can be trusted when giving advice to those who seek it. We can trust only him who has received from God the grace of discrimination and who ... has acquired through great humility and long practice of the virtues an intellect blessed with spiritual insight. Such a man is in a position to advise, not everyone, but at least those who seek him out voluntarily and who question him by their own choice; for he has learned things in their true order.
Then we say: 'Forgive us our trespasses as we forgive those who trespass against us.' Brothers, praying thus, we should very much fear lest the Lord reply to these words of our prayer: 'The judgments you give are the judgments you will get, and the amount you measure out is the amount you will be given.' And you who ask this, see whether you did to no one what you did not want done to you. Therefore before we hear these words of the Lord, brethren, let us first examine our hearts as to whether we are with justice asking of the Lord what we have not denied to those asking us. We ask that our trespasses be forgiven us. God hears and He wants to forgive us, but only if we first pardon those who ask us to do likewise.
There is one method which, if practiced with full attention, will seldom allow anything passionate to slip unnoticed into the heart. This is to examine our thoughts and feelings, so as to discover which they tend: towards pleasing God or towards pleasing ourselves.
To more conveniently become accustomed to remembering God, the fervent Christian has a special means, namely, to repeat ceaselessly a brief prayer of two or three words. Mostly this is 'Lord, have mercy.' or 'Lord Jesus Christ, Son of God, have mercy on me, a sinner.' If you have not yet heard of this, then hear it now, and if you have not done it, then begin from this hour to do it.
Give thanks to God for all things, because thanksgiving is intercession before God for our weakness. Judge yourself always and in everything as a sinner and as one seduced - and so God will not judge you; be humble in everything and you will receive grace.
When God is thanked, He gives us still further blessings, while we, by receiving His gifts, love Him all the more and through this love attain that divine wisdom whose beginning is the fear of God (cf. Prov. 1:7).
Whoever is experienced in the spiritual interpretation of Scripture knows that the simplest passage is of a significance equal to that of the most abstruse passage, and that both are directed to the salvation of man.