I’ve always liked J.I. Packer’s answer from his introductory essay to John Owen’s “The Death of Death in the Death of Christ.”
To the question: what must I do to be saved? the old gospel replies: believe on the Lord Jesus Christ. To the further question: what does it mean to believe on the Lord Jesus Christ? its reply is: it means knowing oneself to be a sinner, and Christ to have died for sinners; abandoning all self-righteousness and self-confidence, and casting oneself wholly upon Him for pardon and peace; and exchanging one’s natural enmity and rebellion against God for a spirit of grateful submission to the will of Christ through the renewing of one’s heart by the Holy Ghost. And to the further question still: how am I to go about believing on Christ and repenting, if I have no natural ability to do these things? it answers: look to Christ, speak to Christ, cry to Christ, just as you are; confess your sin, your impenitence, your unbelief, and cast yourself on His mercy; ask Him to give you a new heart, working in you true repentance and firm faith; ask Him to take away your evil heart of unbelief and to write His law within you, that you may never henceforth stray from Him. Turn to Him and trust Him as best you can, and pray for grace to turn and trust more thoroughly; use the means of grace expectantly, looking to Christ to draw near to you as you seek to draw near to Him; watch, pray, read and hear God’s Word, worship and commune with God’s people, and so continue till you know in yourself beyond doubt that you are indeed a changed being, a penitent believer, and the new heart which you desired has been put within you. The emphasis in this advice is on the need to call upon Christ directly, as the very first step.
“Let not conscience make you linger,
Nor of fitness fondly dream;
All the fitness He requireth
Is to feel your need of Him”
—so do not postpone action till you think you are better, but honestly confess your badness and give yourself up here and now to the Christ who alone can make you better; and wait on Him till His light rises in your soul, as Scripture promises that it shall do. Anything less than this direct dealing with Christ is disobedience of the gospel. Such is the exercise of spirit to which the old evangel summons its hearers. “I believe—help thou mine unbelief”: this must become their cry.