O Heavenly King, Comforter, Spirit of Truth, Who art everywhere present and fillest all things. Treasury of good things and Giver of life, come and dwell in us, and cleanse us of all impurity, and save our souls, O Good One.
The Prayer to the Holy Spirit
On the night before He died, Our Lord at the Mystical Supper gave His last teaching and testimony to His disciples. Among other great and precious promises, He gave them the following: “But when the Comforter is come, whom I will send unto you from the Father, even the Spirit of truth, which proceedeth from the Father, he shall testify of me.” (John 15:26). A few minutes later, after finishing his discourse to the disciples, the Lord lifted His eyes to heaven and prayed to the Father, and when He asked the Father to sanctify the disciples, these were His words: “Sanctify them through thy truth: thy word is truth. As thou hast sent me into the world, even so have I also sent them into the world. And for their sakes I sanctify myself, that they also might be sanctified through the truth.” (John 17:17-19)
Truth, then, is an inseparable attribute of the Holy Spirit Whom the disciples received at Pentecost, when, ten days after the Lord’s Ascension, He fulfilled His promise to send them the Comforter; thus, knowing and believing the truth is prerequisite to true holiness. Christ Himself here states that this was His mission– He sanctified Himself (i.e., He offered Himself to the Father in the Sacrifice of the Cross) that we might be “sanctified through the truth.”
It is popular today to say that theological truth is either unimportant or unknowable, but these ideas do not correspond to the reality of what God is and what human nature is, for God is both Mind and Truth, and man, made in the image of God, has mind; he therefore desires and needs to know the truth in order to be what he is meant to be. Furthermore, God, willing a free and rational relationship with man, has revealed Himself to man in ways that man can understand. Because man is made in the image of God, man has logos - mind, reason, rationality; God has equipped man to know Him. To say that we cannot know theological truth, that "it's all relative" or that "all religions are man-made myths" is to underestimate both God and man gravely.
Man's "equipment" to know God, however, is both limited by nature and damaged by sin. This is why the mind needs grace to "open the eyes of the understanding." Christ sent the Holy Spirit, not only to give the Apostles courage to preach about Him, but also to enlighten their minds about what they were preaching: His Divine Sonship and Incarnation, His saving Death and Resurrection, the mystery of the Holy Trinity, and the mystery of the Church.
We may not, then, say "It doesn't matter," or "I'll believe whatever I want," for we have a duty and a need to "search the Scriptures" diligently, to immerse our minds in the mind of the Church thoroughly, to become more, not less, interested in and convinced of the doctrines of the Orthodox Faith preached by the Apostles and Fathers, and ultimately, if need be, to do what they did, to witness to this Truth even unto death, and thereby by the grace of Christ to inherit the martyrs' crown.
The Dignity and Proper Use of the Mind
For…this is the difference between the rational soul and the irrational, that the irrational is led and governed by the body and senses, whereas the rational soul leads and governs the body and the senses. For it has been ordained by God that the rational rule over the irrational, and the superior over the inferior, and control the latter. This is why, when the rational soul desires something, it does not rush at once to action to gratify the desire, but is hindered by reason, which is the ruler. [St. John] Damascene remarks: “The irrational animals lack the power of free-choice-and-self-control (autoexousion). They are ruled by nature instead of ruling it. Hence they do not oppose their natural appetites. When they desire something, they rush to satisfy their appetite; but man, being rational, rules nature instead of being ruled by it; hence when he desires something, he has the power of restraining the desire instead of following it (St. John of Damascus, On the Orthodox Faith, Book II, c. 44).”