One way? Once saved?

"The first and foremost article is this, that Jesus Christ, our God and our Lord, 'was put to death for our trespasses and raised again for our justification.'  He alone is 'the Lamb of God, who takes away the sin of the world.'"
Smalcald Articles, Part II, Article I. (emphasis added)

"The content of the Gospel is this, that the Son of God, Christ our Lord, himself assumed and bore the curse of the law and expiated and paid for all our sins, that through him alone we re-enter the good graces of God, obtain forgiveness of sins through faith, are freed from death and all the punishments of sin, and are saved eternally."
Formula of Concord, Solid Declaration, Article V, "Law and Gospel"

"In the third place, a disputation has arisen whether good works preserve salvation or are necessary to preserve faith, righteousness and salvation.  This, of course, is a serious and important question since only he who endures to the end will be saved (Matthew 24:13) and 'We share in Christ only if we hold our first confidence firm to the end.' (Hebrews 3:14) . . .  
Therefore, we must begin by earnestly criticizing and rejecting the false Epicurean delusion which some dream up that it is impossible to lose faith and the gift of righteousness and salvation, once it has been received, through any sin, even a wanton and deliberate one, or througth wicked works, and that even though a Christian follows his evil lusts without fear and shame, resists the Holy Spirit, and deliberately proceeds to sin against his conscience, he can nevertheless retain faith, the grace of God, righteousness, and salvation."
Formula of Concord, Solid Declaration, Article IV "Good Works"

I take up two matters this week because it seems to me they are related.  The first is whether faith can be lost.  Can someone have saving faith, but then lose it?  The second is "the exclusivity and universality of the Christ event" (which I assumed below in discussion, but did not provide the reference) and the question of whether a Christian can lose his or her faith. 

This week's Lectionary Bible Lessons includes as a pericope the portion of Peter's first letter in which he wrote, "Baptism which now saves you...."  This phrase ripped out of all context and joined with the false idea that "once saved, always saved" is a major factor, I believe, in the tendency we have to "get the baby done."  At baptism we receive our ticket to heaven, which we get validated at confirmation.  So we're good to go.  Now no pastor would ever say that this is true.  It is clearly not.  But we might like to believe that we have someone in the baptismal fold they are eternally safe. 
NO NO NO.
Faith can be lost.  Luther in "Freedom of a Christian" used the metaphor of a plant that is allowed to die.  The plant was a gift and was received and maybe even cared for in the short term, but if it is not continually cared for, it dies.  Faith is like that.  Faith can die.  (Luther wrote the same in his letter to the Anabaptists.)

I understand that Luther strove mightily for a system in which we have assurance of our salvation because God did everything.  But as I pointed out earlier, in the second and third parts of "Freedom of a Christian" Luther also pointed out that God's saving action requires a response.  Luther's explanation to each of the Ten Commandments begins, "We should fear and love God...."
YES.  We should fear and love God.  One of the responses to God's love in our love to God, is obedience, not out of duty, but out of love.

The two key passages of the Bible are listed in the quotes from The Book of Concord above. 

But here's the thing.  One of the ways people lose faith is to look for another way.  One of the ways we fail in our evangelism is to allow for another way.  Remember, one motivation for sharing The Good News of God in Jesus Christ is that Hell is real.  Eternal life matters eternally.  Jesus said, "I am the way, and the truth, and the life.  No one comes to the Father but by me."  John 14: 6.
The Apostles were willing to die to share the truth that Jesus is THE way and THE truth and THE life.  Here's why that matters.  Conversion to Islam is NOT OK, anymore than conversion to Jehovah's Witness or Mormonism.  We are NOT worshiping the same God.  Jesus IS eternal God.  (Franklin Graham took a big hit in the media for saying publicly what is "certainly true."  We are not worshiping the same God.)  We are called and sent by Jesus, God the Son to proclaim "the exclusivity and the universality of the Christ event."  (Jesus is the ONLY way to heaven; but Jesus is THE way available for everyone.)
(Have you noticed that in every nation founded upon Christian principles that Islam is legal, and in every nation founded upon Muslim principles Christianity - which includes the duty to share one's faith - is illegal? This is not coincidence.)

Let me be clear in conclusion.  This is a free country.  People need to be free to choose whatever religious or spiritual path they choose to follow.  But in a free country we are also allowed to share the truth of Scripture, however unpopular it may be, that Jesus is the only way.  No hate.  No fear.  Grace and Truth.