"Dearly beloved brethren, our best way will be to run briefly through the words which have been read from the Holy Gospel, and thereafter rest for a while quietly gazing upon the solemn subject of this great Festival. This is the day whereon "suddenly there came a sound from heaven," and the Holy Ghost descended upon the Apostles, and, for fleshly minds, gave them minds wherein the love of God was shed abroad and, while without "there appeared unto them cloven tongues, like as of fire, and it sat upon each of them," within, their hearts were enkindled. While they received the visible presence of God in the form of fire, the flames of His love enwrapped them. The Holy Ghost Himself is love whence it is that John saith "God is love." Whosoever therefore loveth God with all his soul, already hath obtained Him Whom he loveth for no man is able to love God, if He have not gained Him Whom he loveth.
"But, behold, now, if I shall ask any one of you whether he loveth God, he will answer with all boldness and quietness of spirit "I do love him." But at the very beginning of this day's Lesson from the Gospel, ye have heard what the Truth saith " If a man love Me, he will keep My word." The test, then, of love, is whether it is showed by works. Hence the same John hath said in his Epistle. "If a man say, I love God, and keepeth not His commandments, He is a liar." Then do we indeed love God, and keep His commandments, if we deny ourselves the gratification of our appetites. Whosoever still wandereth after unlawful desires, such an one plainly loveth not God, for he saith, Nay, to that which God willeth.
And My Father will love him, and We will come unto him, and make Our abode with him." O my dearly beloved brethren, think what a dignity is that, to have God abiding as a guest in our heart Surely if some rich man or some powerful friend were to come into our house, we would hasten to have our whole house cleaned, lest, perchance, when he came in, he should see aught to displease his eye. So let him that would make his mind an abode for God, cleanse it from all the filth of works of iniquity. Lo, again, what saith the Truth " We will come unto him, and make Our abode with him." There are some hearts whereunto God cometh, but maketh not His abode therein with a certain pricking they feel His Presence, but in time of temptation they forget that which hath pricked them and so they turn again to work unrighteousness, even as though they had never repented."—Pentecost Sermon of Pope St. Gregory the Great, 30th Sermon on the Gospels