We see no form. We hear no sound. We feel the touch of no hand. The Spirit does not address any one of the five senses when He creates the soul anew. Spiritual things are spiritually discerned by minds quickened into spiritual life by the omnipotent Spirit, the giver of life. In regeneration the Spirit is inscrutable, His act of new creation is to the subject a fact, a something done in an unfathomable depth below his consciousness. This fact is recognized only by its effects. He knows that he is a new man, that he is fundamentally changed in all his tendencies, that he is released from his accusing conscience, that his past sins are forgiven and that he is no longer cowering beneath the wrath of God, but basking in the sunshine of His love. He no longer thinks of Him as a police judge sentencing him to a deserved punishment, but as a loving Father. The filial feeling has been suddenly and mysteriously inspired in his bosom, and he hears with his spiritual ear new words sounding in his heart, "Abba, Father." Almost involuntarily he utters them with his lips. He is conscious of a spiritual transformation. The personal agent he does not perceive. In fact the personality of your most intimate friend you have never directly seen. Personality is spiritual and is recognized only by its effects — words, smiles and other actions. You may therefore know the Holy Spirit's personality by His works in your own consciousness, as certainly as a son may know his father with whom he has daily intercourse. We say this to show that spiritual knowledge has the same certitude as our knowledge of men and things around us.
Delitzsch writes in "Biblical Psychology," pages 418, 419:
It happens sometimes that the indwelling of Christ and God and His Spirit signalizes itself with such an energy in the believer that the human individual life is overflowed and swallowed up by the divine as a river of delight. . . . In other cases it is certified that the walk of the Christian is in heaven actually ( Phil. iii. 20, compare Zech. iii. 7 ), by the fact that the future glory is not merely revealed to his perception as a subject of hope ( I Cor. ii. 9, 10 ), but is given him for a moment to see and share in by way of foretaste.This is a state of ecstasy, the highest experience of heavenly blessedness and of a knowledge of the mysteries of the kingdom of heaven. The recipe for the attainment of this knowledge is found in Matt. v. 8, Luke x. 22.
— from The Gospel of the Comforter, Chapter 22.