Salvation

"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!” But they have not all obeyed the gospel. For Isaiah says, “Lord, who has believed what he has heard from us?” So faith comes from hearing, and hearing through the word of Christ.

(Romans 10:14-17 ESV)

Why is this passage so hard for us to understand? Paul here, in Romans, is clearly stating that the only way that people can come to a saving belief in Christ is by hearing the word of God preached. Paul uses a reference here to Isaiah 52. The idea that those who bring the gospel to people have beautiful feet is not a new idea. Paul not only draws on his learning from his teachers in Jewish law, but also on the foundation that God had already laid in the Old Testament.
In this passage we see Paul make an argument that has steps in it. If one of them doesn't happen, then they all don't happen. He says that people cannot call on Christ unless they have already believed. This is a very controversial idea in Christianity today. However, this should not be the case. Paul is very clear in these verses. People do not like to think that they have already believed in Christ before they call on him. That takes away from their feeling of having a part in the saving faith that they receive. If you tell a person that they are saved before they repent (call on God) then they have nothing whatsoever that they can boast in. The whole work of salvation then comes down to the sole grace of God and his saving ability.
Through this passage we can see then that God sends forth people to preach the gospel. Those people preach the gospel to people who hear what they are saying. Through the presentation of what they hear, their hearts are moved/sparked/brought to life. Those same people then call on the Lord in whom they now believe. Through this belief they repent and turn from their sin.