The reality of the Spirit within us can be discerned when we have the sense of a fear of God, a conscience which nudges to do what is right, and a longing for God.
Fear of God:
Fear can be a misleading word because we do not mean being afraid of God. What is meant is the highest respect for God because of His greatness and our failing to live up to His likeness. Most people readily accept that there is some supreme bring who has created everything and who maintains everything. Although today there are many atheists who openly promote a world based on science alone which has no God as creator. This kind of thinking can destroy our ability to recognize this aspect of spirit that lives within each of us. Christians know that God is also the Judge and that we must please God out of our love for Him.
Saint Theophan says this about conscience:
Acknowledging itself to be obliged to please God, the soul would not know how to satisfy this obligation, if the conscience did not rule it in this area... This aspect of the soul is the conscience, which indicates what is right and wrong, what is pleasing to God and what is displeasing, which should be done and which should not be.Longing for God:
Most of at have an inner yearning for something that is beyond our full mental understanding. We often mistake this for a desire for things of this world, such as food or other pleasures, or even love of another person.
Saint Theophan says,
This is expressed in the universal yearning for the supreme good, and is more clearly seen also in the universal dissatisfaction with everything created. What does the satisfaction signify? It signifies that nothing created is capable of satisfying the spirit. The spirit comes from God, it seeks God, it wants to taste Him and, abiding in the living communion, and bond with Him, it rests in Him.The distinguishing mark of mankind is Spirit. It is through Spirit that we find the image of God and have the potential to become in His likeness.
Saint Theophan says,
The human soul makes us a little above the animals, while the spirit makes us a little below the angels.This is one of the main aspects of a spiritual life, laboring to reconnect the Spirit with our soul.
Reference:The Spiritual Life by saint Theophan the Recluse, p 62