True faith, saving faith that receives the good news about the Lamb of God who takes away the sin of the world is a faith created in us by the Holy Spirit through the Gospel (Eph 2:8-9).
Why is justification by grace alone, through faith alone, in Christ alone so hard for us to swallow? Why do words like, "unconditional", "freely imputed", and "apart from our works" cause us to roll our eyes, or sigh, or snort in derision? What is it about a limitless, measureless Gospel message that worries us when we hear it? We believe too much of a good thing is bad news. Too much Gospel leads to even more sin. If God just up and declares us righteous for Christ's sake (and He does), where does our personal righteousness belong? If we're expected to believe that on account of Jesus' bloody suffering and death our Heavenly Father declares us washed clean of sin and death in the blood of the Lamb can we at least take some credit for believing it? At least trusting the Gospel promise about Jesus is our work, right?
No, and that's the problem for even the most devout Christian.
True faith, saving faith that receives the good news about the Lamb of God who takes away the sin of the world is a faith created in us by the Holy Spirit through the Gospel (Eph 2:8-9). The preacher sent to deliver this message of salvation for us is sent, not by men or any man, but by God Himself. And the sermon he's sent to deliver is specific: "You are washed, you are cleansed, you are justified by the blood of the Lamb!" And we say, "Amen."
But our amens always come with a caveat. Spirit and Word works in us, in spite of ourselves, to bend our amen away from ourselves, our believing, and our doing toward Christ Jesus. In this is a war between heaven and earth, Spirit and flesh, life and death. Sometimes it's violent, "We want more Law preaching and less talk about what Jesus does for us. The Gospel is all well and good, as far as that goes, but give us more instruction in how to live a Christian life pleasing to God!" At other times it's more passive, "We're not going back to church until that pastor is gone. We're fed up with his constant bawling about forgiveness, and freedom, and 'The Gospel.'"
In the end, it's what kills us. We fight against justification at every turn. We just can't help ourselves. We have to be in control. We must be given a choice whether to accept or reject the Gospel. There must be a system of measures and controls in place to protect us from this unconditional God and His free election of sinners for the kingdom. The Calvary message is too gracious, too inclusive, and too freeing for all the wrong sorts of people. God and men must be held accountable for their decisions otherwise we're just encouraging people to sin more that grace may abound.
Even the most die-hard believer struggles in her flesh with the limitless, measureless forgiveness and life that is declared in the Gospel. "What am I supposed to do with this," she asks. "Enjoy it," He says. "But what if I'm not worthy of this forgiveness?" "You're not, and you never will be, and that's why it's my gift to you!" "But what if I misuse my freedom in Christ to run back to sin or worse, I misuse my freedom and end up killing myself with it?" "You will, but I will never leave you or forsake you, because you are Mine. Believe it. Receive it."
Even when we're not worthy of forgiveness and misuse the freedom won for us by Jesus on Golgotha, God is faithful and uses His freedom to rescue us from sin and death every day and always. That's what it means to be justified for Christ's sake. God doesn't do 'take-backs.' He doesn't cut corners with the Gospel. There's no "You're justified but...," in our heavenly Father's dealings with sinners. There's only His grace, which we receive through the faith He creates in us, to believe and receive the Christ whose shed blood sets us free to be people of God.