Isn't finding Jesus in a passage sometimes challenging for some passages?

But isn't it always worth the effort, as that it has its own reward?
What about finding the practical application in a passage?

e.g. what about in the following?

II Thessalonians 2:3 Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition;

Prophetically isn't this speaking of a coming bad, general apostasy and the antichrist coming on scene?

But for a practical application, a number of years back, I backslid very badly.

My old nature was fully unleashed.

I was worse than I ever was before I was saved.

I didn't become "re-damned", but I fell away, very far from Jesus.

Also, my old nature was revealed for what it is, a "man of sin", in this flesh of mine.

When David wrote:

Psalm 139:23 Search me, O God, and know my heart: try me, and know my thoughts:
  24 And see if there be any wicked way in me, and lead me in the way everlasting.

Did he write that before he wrote Psalm 51?
Did he find out that his flesh was able to sin grievously?
Then, didn't David say the following, at the end of life, long after Psalm 51?

I Chronicles 29:17 I know also, my God, that thou triest the heart, and hast pleasure in uprightness. As for me, in the uprightness of mine heart I have willingly offered all these things: and now have I seen with joy thy people, which are present here, to offer willingly unto thee.

Then at the end of his life, isn't David called the sweet psalmist of Israel, also long after writing Psalm 51?

II Samuel 23:1 Now these be the last words of David. David the son of Jesse said, and the man who was raised up on high, the anointed of the God of Jacob, and the sweet psalmist of Israel, said,
2 The Spirit of the LORD spake by me, and his word was in my tongue.
3 The God of Israel said, the Rock of Israel spake to me, He that ruleth over men must be just, ruling in the fear of God. 

To which someone responded, to the above, in light of Psalm 51:

“Then will I teach transgressors thy ways; and sinners shall be converted unto thee.”

Emphasis on the word “then”