Backsliding is a very old-fashioned word, but it is a Biblical and a descriptive one.
There are as many ways to tell that you are starting to backslide as there are sins (probably).
For me, my first clue is not one that others might suspect.
My first clue to backsliding is not lustful thoughts about people or greedy attitudes about things.
It is, 95% of the time, a hardening of my heart toward a person or a group of people.
There is a surefire test I have found for it, too.
It is usually related to longterm discouragement, seeing a person or a group of people who claim to be Christians but who very much live by the law (i.e., spend their time judging others rather than reaching the lost for Christ).
What happens is I have a sinful response to the sin of that other person/group of people and start mentally holding my breath, waiting for God to set them straight in some dramatic way.
Fact is, sin usually does wind up with some pretty dramatic conclusions. Those who set themselves up as judges of others often have the most dramatic, painful falls as a result (probably that is a natural consequence of their sin that God allows rather than causes. He said our sin will find us out eventually, right???).
But it is sinful for me to hold my breath, awaiting such an event. It discloses the negativity of my own heart toward a brother or sister in Christ whom I should be urging to run to the cross (with everyone else who claims Christ).
In fact, that is the remedy for my backsliding. To let God soften my heart toward that person so that I grieve, rather than secretly rejoice, when he or she publicly falls into painful circumstances.
God says that throughout His Word. Sin will bring natural consequences. Sometimes it brings God’s chastisement, if the natural consequences don’t get the person’s attention first.
But He also tells us not to rejoice or to enjoy it when someone encounters those painful circumstances. It is very bad for our hearts to allow that kind of emotion to rule us. The Germans call it schadenfreude. Rejoicing at someone else’s fall.
It is utterly the mark of my sinful heart when I allow myself to engage in it. No other explanation for it. It is a mark of my sinful heart when I engage in schadenfreude.
As it is the mark of a sinful heart in anyone who does it . . .
God wants us to bear each other’s burdens. That would include being there for each other when we fall, for we all struggle with sin as long as we are in this body here on earth . . .