Search me, O God, and know my heart;
Try me and know my anxious thoughts;
And see if there be any hurtful way in me,
And lead me in the everlasting way.
What the Psalmist is really asking the Lord here is to show him his sin; and having shown him his sin, then to lead him away from that sin. He asks the Lord to examine his heart, his thoughts, and his way of living. In the context of this Psalm we see that the Psalmist understands that the Lord knows all about him, in fact knows everything about him that can be known, even to the point that the Lord knows what he is going to say before it is said. So in the last two verses the Psalmist, in light of that knowledge, asks the Lord to examine him and lead him in His way.
In Romans 8:13 we see that we are to be putting sin, the deeds of the body, to death; or to phrase it as the Puritans would, we are to be mortifying our sin. But the trick for many of us who have been Christians for a while is that while we have dealt with the obvious sins, the overt sins, what is left are the more subtle sins, the sins which are such a part of us that we don't see them for what they are. Sins that we have gotten so comfortable with that we are not sensitive to them. My wife calls them the sneaky sins.
You know, before we can deal with sin, we must confess it as sin; and to confess our sin we must see it for the sin that it is, and call it as such. This is why we must ask the Lord, just as the Psalmist, to show us our sin, and then to lead us away from that sin. This is a prayer that we know the Lord will answer, because He wants us to be holy as He is holy, and He wants us to desire to be holy.
We should never grow complacent in our walk with the Lord, and just because we are not aware of our sin, does not mean that we do not have sin in our life....oh, just the contrary. But it is way too easy to say we know that we still sin while really not pursuing the destruction of sin in our life. We must remember that sin is sneaky and deceitful all the while desiring to have dominance in our life.
So let us be like the Psalmist who trusted in the Lord enough to ask Him to reveal his sin, so he could be led out of that sin, could put that sin to death, could have victory over that sin by power of God. In fact, if you will pray this prayer you will see the Lord reveal to you the sin He most wants you deal with right now.