Summary: Let the Searcher of Hearts lead you in the everlasting way.
Isn’t it interesting, that the Psalmist ends his song with this invitation; “Search me, O God, and know my heart”
Isn’t that kind of like inviting the neighborhood bully to take your lunch, while he’s sitting under a shade tree eating it? Or saying to your boss, “Hey, I’ll work this Saturday if you want me to”, while standing in front of the newly posted schedule that has your name in bold print across the ‘Saturday’ block?
Why invite someone to do what he has already done, is already doing, and can’t be stopped from doing at will anyway? .
Well obviously, there are very good reasons to do that with God, but let me build my argument on the same structure used by the Psalmist.
Psalm 139 (quickview)  begins by establishing God as the Searcher of hearts (vss 1-6), then the fact that trying to hide the contents of our heart from Him is utterly useless (vss 7-18), then contrasting the attitude of the wicked with that of the righteous, as concerns our openness to His searching eye (vss 19-24).
There is not time in one morning session to adequately cover all of Psalm 139 (quickview)  in an expository sermon, so my primary focus is on the one line of verse 23, “Search me, O God, and know my heart”; but you’ll see that all of the Psalm is, in essence, capsulized in verse 23, because all that the Psalmist has said up to verse 23 has been leading up to this invitation.
(first read entire Psalm)
Searcher of hearts:
The Bible tells us that men of old wrote as they were inspired by the Holy Spirit, and that truth is never more evident than in passages like the Psalm before us today.
David could not have known except through observation, personal experience, and the enlightening of the Holy Spirit, the things that he says about God in this psalm.
What David has so eloquently described for us, is God’s Omnipresence, (meaning He is everywhere and there is nowhere that He is not), and His Omniscience, (meaning He knows everything and there is nothing to be known that He does not know).
We New Testament Christians do not need to take David’s word for it alone however, because the same Holy Spirit has pointed to Christ and revealed these same truths to us in Him and through Him.
In the 6th chapter of Luke’s gospel we find Jesus standing in a Capernaum synagogue, midst a group of hostile Pharisees who are waiting for Him to heal a man with a withered hand so they can accuse Him of working on the Sabbath.
Vs 8 says, “But He knew what they were thinking, and He said to the man with the withered hand, ‘Rise and come forward’!”
In chapter 11 of the same gospel the Pharisees are again seeking to find fault with Jesus and again we are told that He knew their thoughts.
Then I direct you to John 2:24 (quickview) ,25. It looks on the surface like Jesus has a large and faithful following of those who have witnessed His miracles and heard His teaching. But John writes, “...Jesus, on His part, was not entrusting Himself to them, for He knew all men, and because He did not need anyone to bear witness concerning man for He Himself knew what was in man.”