One of the plainest lessons about backsliding is found in how Israel and Judah slid downward from their place as God's chosen people - a lesson that ultimately applies to spiritual Israelites (see Daughter of Zion).
"The Lord said also unto me in the days of Josiah the king, Hast thou seen that which backsliding Israel hath done? She is gone up upon every high mountain and under every green tree, and there hath played the harlot. And I said after she had done all these things, Turn thou unto me. But she returned not. And her treacherous sister Judah saw it [see also Sisters of Sin]."
"And I saw, when for all the causes whereby backsliding Israel committed adultery I had put her away, and given her a bill of divorce; yet her treacherous sister Judah feared not, but went and played the harlot also. And it came to pass through the lightness of her whoredom, that she defiled the land, and committed adultery with stones and with stocks. And yet for all this her treacherous sister Judah hath not turned unto me with her whole heart, but feignedly, saith The Lord."
"And The Lord said unto me, The backsliding Israel hath justified herself more than treacherous Judah. Go and proclaim these words toward the north, and say, Return, thou backsliding Israel, saith The Lord; and I will not cause mine anger to fall upon you: for I am merciful, saith The Lord, and I will not keep anger for ever. Only acknowledge thine iniquity, that thou hast transgressed against The Lord thy God, and hast scattered thy ways to the strangers under every green tree, and ye have not obeyed my voice, saith The Lord."
"Turn, O backsliding children, saith The Lord; for I am married unto you: and I will take you one of a city, and two of a family, and I will bring you to Zion [see Who, What or Where Is Zion?]" (Jeremiah 3:6-14 KJV)