St. Philaret of Moscow
We celebrate the coming of the Holy Spirit… Could it be that there was no Spirit in us? No, there was not: For the Holy Ghost was not yet given (Jn. 7:39). And a new spirit will I put within you (Ez. 36:26); God breathes a new spirit of life into man… The apostles were the first vessels of the Holy Spirit… As life in plants freezes from the winter cold, so does man’s spirit freeze when he is given over to sin… There is a sprout of life in a seed, and life is also in plants that have frozen over the winter. But if the Lord does not send the spirit of spring, the seed and the plant do not grow, and the face of the earth is not renewed (cf. Ps. 103, 30)… Repentance opens the door to the operation of the Spirit of God, but a lack of repentance locks that door…
And then the soul enlivened and cleansed by the Holy Spirit shines with the Trinitarian unity… We cannot fathom how this wondrous work of goodwill takes place, but the Word of God is true… Here is the path by which the Spirit of God leads to perfection those who receive Him … The beginning of it all is repentance, the middle of this work and ascetic struggle is cleansing of the heart from passions and its saturation with virtues, and the end is the holy mystery of communion with God… Where there is no communion with God, there is no Spirit… For whatsoever a man soweth, that shall he also reap. For he that soweth to his flesh shall of the flesh reap corruption; but he that soweth to the Spirit shall of the Spirit reap life everlasting (Gal. 6:7-8).
St. Theophan the Recluse
When the Most High came down and confused the tongues, He divided the nations (kontakion of Pentecost)… The Lord confused the languages of those nations that were building the Tower of Babel… People had conceived the plan of reaching the heavens through this building… They wanted to be comparable to God in power, to elevate themselves… The Lord defeated this plan, for pride lay at the foundation of it… When on the day of Pentecost He divided the tongues of fire over the heads of the apostles, the entire Christian world was called to unity… To what unity does the Lord call us? To the unity of faith, of truth, of sanctity, and to the highest form of unity—unity in Love.
St. Luke (Voino-Yasnetsky)