To backslide is to allow oneself to go back once more into sin. It is often more difficult to revert to being good because the help from the Light is often in this case not available. If one has been allowed to see the Light and Truth, the responsibility is often enormous and one is accounted ten times more guilty than those without this knowledge if one allows oneself to give in to temptation.
If one has been allowed to reach a particular spiritual height, the fall from that height is often devastating. It is equivalent to physically falling from a tall building; the impact is shattering, even fatal. It is the same spiritually whereby such a one is often not able to recover spiritually from his fall. We should therefore be mindful so that we treat the Truth given to us with the utmost reverence.
We live in a material world where evil has the upper hand at the present moment and we will be tempted. We therefore should be doubly alert so as not to fall into these temptations. If we are truly alert and are constantly spiritually watchful, then it would be more difficult for us to fall into temptation, let alone completely backslide.