The kingdom of God is within you (Lk. 17:21), said the Lord; that is, in the heart. Therefore, it is necessary to seek it out in the heart, cleansing it of the passions and assaults of the enemy, judging and reproaching no one…—St. Macarius of Optina
The beginning of our salvation lies in a sincere comprehension of our sinfulness and the self-reproach and humility before God and people that follow as a result. A heart that is broken and humbled God will not despise (Ps. 50:19). In addition to this, it is necessary to deny ourselves (Mk. 8:34), that is, to reject our own will and understanding and to obey our superiors and mentors, as the holy fathers teach.