Election is not according to God's hidden will, but revealed in Jesus. God chooses us in Jesus. Our salvation is not a matter of God sovereignly choosing is and isn't saved, but God choosing us in His grace.
This is fundamentally different. In the Calvinist system, God picks some to be saved, and thus there are some not chosen for salvation. That is not the Lutheran position--God does not look past, overlook, or choose anyone not to be saved--Christ died for everyone, and God's will and desire is that everyone be saved.
The point isn't that God says only some can be saved.
The point is that God is the One who comes to us to save us in Jesus; and He does this for the whole world.
Of course God doesn't will for man to sin. Sin is contrary to the will of God. God is not the author of evil.
The difference is that God's election is not by some hidden, inscrutable, sovereign choice; but by grace through the Incarnate Logos.
That isn't the Lutheran opposition, the Lutheran opposition to synergism is that attributes to man works which contribute to his salvation. It's not that it detracts from God's glory, but that it detracts from God's grace. When the Lutheran confesses that salvation is by grace alone, we mean that in the most absolute of terms: Grace alone. It is God who comes down, not we who go up. It is God who meets us, not us meeting God half way. It is God, in His mercy, kindness, and love embracing the humility and shame of the cross that rescues us, makes us right with God, and heals us.
It is intrinsically about making a firm distinction between Law and Gospel. From Luther's Heidelberg Disputation: "The Law says 'Do this' and it is never done. Grace says 'Trust this' and it is already done." The Law commands that which is good and right, and reveals that we are not righteous, but sinners; the Law is therefore unable to save us. No one can be righteous according to the Law, except One: Jesus Christ by whose righteous obedience has undone Adam's disobedience, by His death and resurrection crucifies sin and death and heals us, justifying us before God, and uniting us to Himself and to His life as pure gift, so that we have in Him sonship, by which we are heirs of God, joint-heirs with Jesus, and by the Spirit cry out, "Abba! Father!" and are made partakers of the divine nature, by grace, ultimately to the fullness that we will have in the resurrection of the dead, the eternal and immortal life in the Age to Come.
Lutheranism speaks of the distinction between Coram Deo and Coram Hominibus; that is us before God and us before our fellow human beings. To put it another way, God doesn't need our good works, but our neighbor does. God does not benefit from our good deeds, but our neighbor does--because they have hungry mouths to feed, they are thirsty and need drink, a roof over their head. The Law of God calls us outward, in love, toward others, in service to Jesus Christ, to live lives as living sacrifices to God. Our sacrifices, however, do not improve our status before God, it does not improve our station before God--the love and grace of God which He has for us in Jesus, which we have received in full from Him, received in faith through Word and Sacrament is truly, and indeed, full. We can't win brownie points with God, we can't make Him love us less, and we can't make Him love us more--He loves us fully, perfectly, and completely because, as St. John reminds us, God is love.
So what are our good deeds for? Are they for God? No, they are for our fellow man. Nothing we can do can increase, improve, or contribute to what God has already done for us, and already gives us. For He gives us the fullness of Himself in Jesus, the love we have, the grace we have, the salvation we have from Him is perfect and complete; for Christ died for the whole world. As St. Paul says, by grace we have been saved, not by our efforts, so that no one may boast; but we have been created for good works which have been prepared for us, that we might walk in them (Ephesians 2:10). The good works we do are not to improve our place before God, as though God rewards us based on our merits; but rather the works we do we do out of love for God and in response to the great love He has for us, and we do them for the sake of our neighbor.
Good works aren't that we might be saved, but rather we have been saved for good works.
We say it is monergistic because man is a passive recipient of God's mercies. Man does have a role to play in the living out of his faith, the living out of his salvation in the grace and love of God--that is the Coram Hominibus dimension of our Christian life. Christianity is not a purely vertical experience--us and God. It is also a horizontal one, us and other people and all of creation. Salvation comes solely from above, from God, down to us, as grace; but this grace and this life we have received is to be lived out in sacrifice and service to others. The Lutheran distinction is to say that the Coram Hominibus dimension of Christian life is not about our contributing to our salvation (what we have received from God) but of living that salvation out in response to God's grace.
This isn't the Lutheran position, however. God doesn't choose to damn anyone. God damns nobody. Since it is God's will that everyone be saved, Christ died for everyone. We damn ourselves. God is not unjust, since He does not pick and choose who will and won't be saved; God is just and the justifier of the unjust.
God alone saves.
Man alone damns.
To quote C.S. Lewis, "There are only two kinds of people in the end, those who say to God, 'Thy will be done.' And to those to whom God says, 'Thy will be done.'"
St. Isaac the Syrian speaks of two kinds of people in the end, those who experience the love of God as blessedness, and those who experience the love of God as anguish--but God deprives His love from no one, for love is impartial, and God's love is for everyone. The distinction isn't God's disposition toward us, but our disposition toward God. What the Lutheran says is that our disposition toward God changes, not by our own will, but by God's grace which comes to us through the Gospel, granting us faith.
Why then are some damned? Not by God's decree, will, or choice--but by man's own sinful, willful choice. It is man who chooses his own destruction. It is God's will that he be saved and live and have life abundantly in the Age to Come.
-CryptoLutheran