"Simon Peter, a servant and apostle of Jesus Christ,
To those who through the righteousness of our God and Savior Jesus Christ have received a faith as precious as ours:" (2 Peter 1:1). "Faith" here is not "the faith," the apostolic doctrinal deposit. It is trust in God's saving work through Jesus the Messiah, and the recipients of this letter, like Peter and the apostles, had also obtained such a faith. Notice that this faith is (a) received from without, not conjured up from within; and (b) it is procured solely through the righteousness of Jesus Christ. Faith itself seems to be a gift obtained by Christ for his people through his atoning work on the cross.
This is the reality of the grace of God, expressed so boldly in the words of John Owen: "To suppose that whatever God requireth of us we have power of ourselves to do, is to make the cross and grace of Jesus Christ of none effect." Even the faith which God requires of us for justification and life is a gift from his gracious hand. The apostle Paul knew this, that the whole of his salvation was of grace, and not just the offering to him of Christ. Its reality burned in his heart, and it turned his life into a life of gratitude.
"For who makes you different from anyone else? What do you have that you did not receive? And if you did receive it, why do you boast as though you did not?" (1 Corinthians 4:7 NIV). Everything we have is a gift received from without, coming down from heaven (James 1:17). On this basis, Paul admonishes the Corinthians, who boasted of their spiritual superiority over others, because even their very own Christian spirituality itself was an undeserved blessing.
Later in this same letter, Paul expresses that only by God's grace is he a faithful apostle: "But by the grace of God I am what I am, and his grace toward me was not in vain. On the contrary, I worked harder than any of them, though it was not I, but the grace of God that is with me" (1 Corinthians 15:10). Paul knew that he didn't deserve to be a saved sinner who knew and cherished (believed in) Jesus; but he was such "by the grace of God." And this same grace is what turned him into the bold missionary he had become.
I know I haven't addressed how such a God-given faith can be required of us, nor how faith is still our own faith and an act of our own will and volition. These are tricky questions, but I believe the Bible gives an answer to both of them. But I hope you see that the very fact that you ever "made a decision for Christ" or "accepted Jesus as your Savior" or "committed yourself to Jesus as Lord" is itself a work of God's goodness and love in your life when you were dead in sin and alienated from him. It was God's arms reaching out to embrace you long before you ever reached out to embrace him. And because of such--because salvation rests not on the strength of your decisions and commitments but on the grace and saving purposes of God--you can rest secure in his love.