I haven't had time to finish my post on the cure for backsliding, so until then (I'm aiming for tomorrow) here's a taste of John Owen from Vol. 1 of his works.
Have you, in the way of your profession, had any experience of these spiritual decays? I doubt not but that there are some who have been preserved green and flourishing from their first conversion unto God, who never fell under the power of sloth, neglect, or temptation, at least not for any remarkable season; but they are but few. ...[There are examples of Old Testament saints] who have obtained relief and deliverance from under their decays, — whose backslidings have been healed, and their diseases cured. So it was with David, as he divinely expresseth it, Ps. 103. 1, 3–5, “Bless the Lord, O my soul; and all that is within me, bless his holy name. Who forgiveth all thine iniquities; who healeth all thy diseases: who redeemeth thy life from destruction; who crowneth thee with loving-kindness and tender mercies: who satisfieth thy mouth with good things, so that thy youth is renewed like the eagle’s.” So does he celebrate his deliverance from that state whereof he complains, Ps. 38., — which we mentioned before.
And there is no grace or mercy that does more affect the hearts of believers, that gives them a greater transport of joy and thankfulness, than this of deliverance from backslidings. It is a bringing of the soul out of prison, which enlargeth it unto praise, Ps. 142. 7. Of this sort I doubt not but that there are many; for God has given great warnings of the danger of a spiritually-decaying state; and he has made great promises of recovery from it; and multitudes in the church are daily exercised herein.
The work of recovering backsliders or believers from under their spiritual decays is an act of sovereign grace, wrought in us by virtue of divine promises. Out of this eater comes meat. Because believers are liable to such declensions, backslidings, and decays, God has provided and given unto us great and precious promises of a recovery, if we duly apply ourselves unto the means of it.
John Owen, Meditations and Discourses Concerning the Glory of Christ, Applied