“This is why the Lord promised to send the Holy Spirit: He was to prepare us as an offering to God. Like dry flour, which cannot become dough and one loaf of bread without moisture, so we who are many could not become one in Christ Jesus without the water and Spirit that comes down from heaven. Through the Baptism that liberates us from change and decay we have become one in Christ’s Body; through the Spirit we have become one in His Life.” (St. Irenaeus)
We could never know anything about Christ or believe in Him and receive Him as our Lord if it were not first offered to us and laid on our hearts by the Holy Spirit through the preaching of the Gospel. The redemptive work has taken place and is finished, for Christ has purchased and won the treasure for us through His suffering, death, resurrection, etc. But if that saving action stays hidden and no one knows about it, then it would all be for nothing, wasted. In order that this treasure might not remain buried but be taken up and enjoyed, God has let the Word go forth and be proclaimed. In the Word He has given us His Holy Spirit to lay the treasure of redemption on our hearts and make it our very own. (Luther’s Large Catechism
On the day of Holy Pentecost we celebrate and thank our dear Lord God for the great and timeless gift which He bestowed one earth. From heaven He revealed to us poor earthlings his holy, precious Word—a Word that is neither common nor ordinary. For it was on this very day that Christ established His kingdom through the apostles, a kingdom that through the gospel is revealed to the whole world. Christ possessed this kingdom in his own person from all eternity, but on this day the Holy Spirit used the apostles to reveal it to all the world. And this revelation was made with great courage, boldness, and joy by the apostles. (Blessed Martin Luther)
Today the Holy Spirit came upon the disciples with a sudden sound, and completely changed their earthbound way of thinking by his love. When tongues of fire appear outwardly, their hearts within them were set afire. Since they received God in a vision of fire, they were gently enflamed by love. The Holy Spirit is love, and so St. John says: God is love. A person who desires God with his whole heart already possesses the one he loves. No one could love God unless he possessed the one he loves. If any one of you should be asked if he loved God, he would answer with entire confidence and complete conviction, “I do.” But you hear at the beginning of the Gospel reading what Truth says: “If anyone loves me, he will keep my word.” The proof of love is its manifestation in deeds. (Gregory the Great)