In the past God spoke to our ancestors through the prophets at many times and in various ways, but in these last days he has spoken to us by his Son, whom he appointed heir of all things, and through whom also he made the universe (Hebrews 1:1-2).
The author of Hebrews tells us here that, what God wanted to communicate to mankind, he has communicated finally and completely through Jesus Christ. In the past, from the Fall of Man until Christ, God the Father used many different ways to communicate with man. In the Garden of Eden he spoke to man directly. He spoke to the patriarchs by appearing to them as the Angel of the Lord. He spoke to Moses through a burning bush, and through a cloud on a mountain. He spoke to the prophets in dreams and visions. The message was always the same throughout all that time: That he would redeem mankind from their fallen state by His grace through faith in Christ, and restore creation. But in these last days, the writer of Hebrews says, he has spoken to us by His Son.
The message of the entire Bible is God saving mankind from sin, death, and devil by the atoning work of Christ. St. Augustine explained, “The New [Testament] is in the Old [Testament] concealed; The Old is in the New revealed.” This is the message God was communicating to man after the Fall in the Garden, and this is the message He communicates to us now.
Whenever God is speaking to us, however, he speaks to us by his external word. What I mean is this: God comes to man “externally,” through means. He communicates to us though words, using human language that men are capable of understanding. He uses physical elements and uses his word to connect his promises to them, and to deliver those promises to man. He does not work in man through “burnings” in the bosom. He does not work redemption in man apart from His word. St. Paul writes in Romans:
Consequently, faith comes from hearing the message, and the message is heard through the word of Christ,” (Romans 10:17).
The burning bush, the visions, all the other means by which God communicated the Gospel to man, were means of delivering to man the external word. And now, in these last days, God has spoken to us through Christ. God’s communication with man has been concentrated down to Christ’s atoning death and resurrection. It is finished, and there is no longer any need to burn bushes or send visions to prophets. God has spoken to us by his Son – the Word incarnate, who bled and died on the cross of Calvary to atone for the sins of the world. This word, the message of Christ, has been collected for us into the volume of Holy Scripture we call the Bible. When you read the Bible, you hear God’s voice. It is God who speaks to you through those words on the page. When you hear faithful preaching, it is God who speaks to you, through the voice of that faithful pastor. When you receive the Sacrament of the Altar you hear God’s word of promise – given and shed for you, for the remission of sins – and faith takes hold of that promise, connected with those physical elements of bread and wine.
Martin Luther in his day dealt with “enthusiasts,” or people who believed that they received the Spirit and faith without God’s word, i.e., by some mystical divine “inner revelation.” The world is no less full of people today who deny the efficacy of Holy Scripture, yet claim that God has given them some new revelation or inner illumination allowing them to ignore what Scripture teaches. All you have to do is turn on Trinity Broadcasting Network and you will see a parade of preachers preaching, not the Word of God as delivered to us in Holy Scripture, but a word that they have received from some personal revelation. What Luther had to say about enthusiasts is equally appropriate for us today.
He [the devil] led them [Adam and Eve] from God’s outward word to spiritualizing and self-pride. And yet he did this through outward words. In the same way our enthusiasts today condemn the outward word. Yet they themselves are not silent. They fill the world with their babbling and writings, as if the spirit could not come through the Apostle’s writings and spoken word, but has to come through their writings and worlds. Why don’t they leave out their own sermons and writings and let the Spirit himself come to people without their writings before them, as they boast that He has come into them without the preaching of the Scriptures?  (Luther).
The Gospel is the means by which the Holy Spirit offers us all the blessings of Christ and creates faith in people. The written and spoken (preached) word of the Gospel, as well as the sacraments – God’s word of promise connected to bread and wine, and water – are the means of grace.
Lest I be accused of “putting God in a box,” I must clarify that I am not saying it is impossible for God to impart divine revelations today, or that it is impossible for God to convert men apart from his word. I’m simply saying that he does not wish to. God has always dealt with man through means, and he expressly tells us that it is his will to do so. So, while it is indeed possible for God to send man a “burning in the bosom,” we shouldn’t expect him to do so, because he has told us that he doesn’t operate that way. Many mistakenly take their intense feelings, worked up in a religious frenzy, as a way to assure themselves that they are in the faith. Feelings change, however, and should certainly not be used as a basis for assurance of faith. Furthermore, anyone who claims that he has received a divine revelation should be tested against what we know for certain to be divine revelation – Holy Scripture. Whatever is not in accord with Scripture should be soundly rejected. Luther comments:
In a word, enthusiasm inheres in Adam and his children from the beginning [from the first fall] to the end of the world, [its poison] having been implanted and infused into them by the old dragon, and is the origin, power [life], and strength of all heresy, especially of that of the Papacy and Mahomet. Therefore we ought and must constantly maintain this point, that God does not wish to deal with us otherwise than through the spoken Word and the Sacraments. It is the devil himself whatsoever is extolled as Spirit without the Word and Sacraments. For God wished to appear even to Moses through the burning bush and spoken Word; and no prophet neither Elijah nor Elisha, received the Spirit without the Ten Commandments [or spoken Word]. Neither was John the Baptist conceived without the preceding word of Gabriel, nor did he leap in his mother’s womb without the voice of Mary. And Peter says: The prophecy came not by the will of man; but holy men of God spake as they were moved by the Holy Ghost . Without the outward Word, however, they were not holy, much less would the Holy Ghost have moved them to speak when they still were unholy [or profane]; for they were holy, says he, since the Holy Ghost spake through them (Luther).
We should marvel at how God deals with us. Not only has he redeemed us by His grace, through faith alone in Christ, He has given us his external word, by which we can be certain of God’s promises of forgiveness and eternal life, even when we feel the weight of our sin, and do not feel “saved.” That can sustain and comfort us when our bosoms cease to burn, our inner illumination goes dim, and we remember what kind of rotten sinners we are, undeserving of God’s favor. In those times we can look to God’s external word; whether in Scriptures, in the preaching of a faithful pastor, or in the Lord’s Supper or remembrance of our Baptism, and have assurance that though we are sinners, God has forgiven us for Christ’s sake, and is faithful.
Luther, M. (n.d.). The Smalcald Articles. Retrieved December 04, 2014, from The Book of Concord: The Confessions of the Lutheran Church: http://bookofconcord.org/smalcald.php#confession
 SA III VII 5-6
 2 Peter 1:19-21