According to the reformed way of thinking, humanity’s basic problem is our distance from God. The problem more specifically is that our distance from God is sinful – it is our sin, I suppose – and it is characterised by a such preference on our part for maintaining this distance between us and him that we disable ourselves from ever beginning to make a move towards him.
It’s into this situation that the gospel message comes, to offer the hope of reconciliation to every sinner distanced from God by their sin. The briefest possible summary of the gospel message that I can imagine is just, “There is a Saviour for sinners,” but of course there needs to be more information than that. The precise nature and extent of the sinfulness of these sinners is one area which needs further elaboration (although here I’ll just refer you to this and this part of scripture without going into too much detail). We also need to know more about the identity of the Saviour – fundamentally that he is the Son God in human nature (Luke 1:35, eg), and perhaps some other things, the more the better, such as the fact that he acts as Saviour with God’s approval, and has all the qualifications necessary in a Saviour of sinners.
But in addition to this, we need to know how sinners, and the Saviour provided for sinners, can meet. It’s one thing that there is a Saviour, but how can he be my Saviour? It’s in God’s infinite grace that he does provide a Saviour, but if I myself personally am to benefit from that provision, there has to be a way that he becomes not only available to me but actually possessed by me.
Of course, you can’t tell the whole story without explaining God’s part, and how God puts his provision into the possession of the sinner. But I’m only talking about our side of the story, and on the part of the sinner what is required is faith.
And it is faith specifically that is required for a sinner to be saved. When the question is asked directly, ‘What must I do to be saved?’ the answer is straightforwardly, ‘Believe on the Lord Jesus Christ and thou shalt be saved.’ That is, ‘by grace ye are saved through faith’ rather than anything else; ‘The scripture saith, Whosoever believeth on him shall not be ashamed. For there is no difference between the Jew and the Greek, for the same Lord is rich unto all that call upon him. For whosoever shall call upon the name of the Lord shall be saved. How then shall they call on him in whom they have not believed?’ (References here, here, and here.)
Clearly, as sinners, prior to conversion, we are lacking in every grace – not just faith, but also love, and obedience, and patience, and godliness, and brotherly kindness – we are guilty for our sins of omission and commission in all these areas and more. And the Christian (the sinner, in other words, who is saved) is expected and duty-bound to show evidence of all these things, and is obliged to grow in grace in every way. But without faith, it is not possible either to have or to grow in any of these other graces.
It presumably goes without saying that people who don’t love the Lord cannot be saved, and that the same holds for those who don’t obey or worship or repent towards the Lord. But faith is necessary for salvation in a unique way – as the one grace which, by taking hold of the Saviour, closes the sinful distance between the sinner and the Saviour, and puts the sinner in a state of reconciliation with God who they have offended. What faith is, in other words, is the means of connection between the graceless sinner and Christ the gracious Saviour who saves graceless sinners.
Before there can be any spiritual life in the soul, then – before the soul is saved, and before there can be any sign of these other graces which always accompany faith – the soul needs to make contact with the Saviour by faith, and any kind of faith that falls short of uniting the sinner to the Saviour cannot be a saving faith.