God has shown us no other way by which we can come into heaven than through His precious Word, the Holy Gospel. Whoever gladly and diligently hears and receives it, and who loves and delights in it, will be helped. That is the one miracle that daily still takes place in Christendom, that our ears, which the devil stopped up through sin, are again opened by the Word, so that we receive it.
If we are to be loosed from the devil’s bonds, and possess ready tongues and good ears, this can happen only through the external Word and preaching, through external means. We must, first of all, hear the Word, not neglecting Baptism or the Sacrament either, and the Holy Spirit will then by present to free the ears and tongues. Therefore, we must be on guard against the fantastic spirits who despise the external Word and Sacrament, waiting till God speaks to them in the heart. No, says Christ, here is my finger, the external Word, which must sound in the ears; my spittle, which must moisten and bestir the tongue; in this way my work proceeds rightly and readily from place to place. We see this wherever the external Word has free course; there true Christians will be found. Wherever it does not have free course; there true Christians will be found. Wherever it does not have free course, there none will be found, for as goes the shepherd, so the sheep. Everyone should take care, therefore, to be found on this path and gladly hear God’s Word. Without the Word, God does not reveal Himself in your heart. To see and know Him can happen only through the external Word and Sacraments. The Holy Spirit works in no other way.
(Both quotes are from Luther’s House Postils)