When God gave His Law, He knew man could not keep it. The Law always condemns. In this world, after the Fall, man cannot keep the Law. It will always and only show where we have stumbled. It tells us what we ought to do, that which pleases God. But the Law is also supposed to drive us to our Savior, our only source of Help and Comfort. Condemned and killed by the Law, we flee to the Gospel, to the Christ revealed in it who "takes away the sin of the world."
To go to God uncovered, unprotected is to die. To have no intermediary between you and God means you are approaching God on your own, standing on your own merit. The man in whom the Law has worked wouldn't dare go to God uncovered. He knows his unrighteousness and, until he is covered, does not approach the Almighty.
So in the people of Israel, having heard God's holy Law, we see what the Law does. They were afraid. They knew they had not kept God's Law, and because of their flesh they knew they never could. So they keep their distance. They ask that God only come to them in grace, through His chosen intermediary. They know that hearing God on their own, without Moses, is to die.
Unfortunately, Israel did not stay this way. They went the way of all flesh in its delusion. They replaced God's Law with laws of their own. All of God's Laws were replaced with countless attainable laws, designed to make Israel feel righteous. And with God's Law thrown out, they went to God uncovered, without their intermediary. They approached everything as if they were righteous and godly, when all they did was worship themselves. They fell under Jesus' just condemnation, "These people draw near to Me with their mouth and honor Me with their lips, but their heart is far from Me. And in vain they worship Me, teaching as doctrines the commandments of men."
How often are we the same hypocrites as Israel? How often are we outwardly righteous, saying pious-sounding things only to mask what is really in our hearts? We claim to honor father, mother, and other authorities; we claim to love our neighbors as ourselves; we claim that we are without sexual impurity; we claim we are without covetousness. But our actions betray us. We are not as pure as we claim to be. What comes out of us, especially when we think no one is looking, shows the evil that has corrupted us, that defiles us.
Fortunately God does not "deal with us according to our sins or punish us according to our iniquities." Instead He is gracious and merciful. He has considered our trouble, and despite our evil thoughts, adulteries, murders, and blasphemies, He has delivered us in His righteousness. You are delivered because Christ was handed over. He was given in your place, and all your wickedness was heaped upon Him. "What punishment so strange is suffered yonder. The Shepherd dies for sheep who love to wander. The Master pays the debt His servants owe Him."
And in Christ’s paying of your sin, you are covered. You are covered by the Blood shed on the cross. That Blood was at work in the Font, when the Blood-tinged waters, with God’s Word, made you His dear child. And thus covered, you can now stand before God without fear or shame. The smoke and fire and lightnings are quenched by these waters and you are safe in the presence of God because the Blood of Christ is your intermediary, and one that will not fail or leave you.
Now that you are safely in Christ to all eternity, you need not fear. You can approach God; you need not stand afar off. Rather, Christ beckons you this day. He calls you here, to the mountain of His holy Altar so you may again receive His Blood to cover you, to forgive you, and to sustain you in all the world’s strife. Come, be glad and rejoice in the infinite mercy of Almighty God given in bread and wine, Body and Blood.
Why does the Pastor preach? Scripture explains that the role of preaching the Word of God is how saving faith is created: “How then will they call on Him in whom they have not believed? And how are they to believe in Him of whom they have never heard? And how are they to hear without someone preaching? And how are they to preach unless they are sent? As it is written, ‘How beautiful are the feet of those who preach the good news!’ … So faith comes from hearing, and hearing through the Word of Christ” (Romans 10:14-17). The Augsburg Confession, seeing this connection between the Preaching Office and saving faith, summarizes Scripture on the Office of the Holy Ministry in this way: “To obtain [saving, justifying] faith, God instituted the Office of Preaching, giving the Gospel and the Sacraments. Through these, as through means, He gives the Holy Spirit who produces faith, where and when He wills, in those who hear the Gospel. It teaches that we have a gracious God, not through our merit but through Christ’s merit, when we so believe” (AC V 1-3). The whole reason the Pastor preaches is so saving faith can be created, so we know that “we have a gracious God” who loves us and has saved us from our sin by the death and resurrection of Jesus Christ.