From the additional notes to Charles Spurgeon's The Treasury of David, Psalm 107
Verse 43. Will observe these things, etc. Will carefully note and remark what is here said of the fall and recovery of mankind, of our state by nature and by grace. True wisdom consists in observing these two things, what we are in ourselves, and what we are in Christ; in a deep sense of our misery by sin, stirring us up to seek our remedy in the Redeemer. This is wisdom. And whosoever is thus wise unto salvation shall understand the lovingkindness of the Lord; shall be able to apply what he understands of it to his own private use and benefit.
The verb in the original rendered "shall understand", is in the conjugation called Hithpael, which signifies to act upon itself. Whosoever observes those things properly finds his own interest in them. He makes the understanding of them useful to himself. He does not study them as a science or theory, but as interesting points in which he is nearly concerned, and which he therefore tries to bring home for his own private advantage. When he hears of the mercies of the Lord Jesus recorded in this psalm he desires to partake of them. When he hears of the great deliverances vouchsafed to sinful ruined man, he studies to have his own share in them. What is said of these persons who wandered out of the way in the wilderness, and fell into the bondage of sin, and were afflicted with its diseases, and troubled like a stormy sea, with its continual tempests; all this he knows was his own case, and therefore what follows of their flourishing state after Christ delivered them may be his also if he cry unto the Lord, as they did, for help.
And he never ceases praying and seeking, until the blessed Jesus brings him to the haven of the church, where he would be. And if he find the church diminished and brought low, he is not discouraged; but relies on the promises of his God, who will set him on high out of the reach of public calamity, when he comes to destroy an infidel church. He observes what is said on this psalm concerning those things; and he knows it to be true, by his own experience. And therefore the lovingkindness of the Lord here recorded is to him a subject of exceeding great joy, because he has tasted of it. Whoso is wise will bring his knowledge of this psalm home to his own heart, and he shall understand the lovingkindness of the Lord, he shall be able to apply what he understands to his own benefit, and shall therefore be continually praising the Lord for his goodness, and declaring the wonders which he hath done for the salvation of men.—William Romaine.