(Prov 3:5) Trust in the LORD with all thine heart; and lean not unto thine own understanding.
(Prov 3:7) Be not wise in thine own eyes: fear the LORD, and depart from evil.
People have departed from the faith simply because they were proud and thought they were able to run their own life. They feel they are strong enough to wage this spiritual war on their own. They needed the Lord to save them but from here on they could handle it.
Solomon tells us not to trust our own understanding and strength. We are finite creatures with very limited knowledge and understanding. The oldest of us have lived only a century and most less on this earth. We may have had a broad background of experience in life, but there is none that have enough wisdom, understanding or knowledge to make it on our own.
Peter warns of the devil walking about seeking whom he can devour because his stealth is as that of a lion. Lions are large, strong, quick and very clever predators. They are able to see at night and can move softly through the terrain and come upon their prey by surprise. If they can sneak up on other animals, then they certainly can sneak up on us humans. In the same way, the devil is able to take us by surprise. A pride of lions uses their cunning to overtake their prey. Old lions that have been around a while and are no longer able to be “king” of the pride are still part of it. They have lost many of their teeth and are not as able to catch fast moving prey as the younger ones. But he can roar very loudly and with much intimidation. So he will approach very noticeably some nice looking prey and roar loudly at them. The unsuspecting prey will run away from him but the young lions have positioned themselves in the direction they will be running and they run right into their grasp. After all the others have finished eating to their full, they permit the old lion to satisfy his hunger.
In similar ways the devil will attack us and if we are trusting in our own wisdom and strength, then we may well become a captured prey. The devil has had thousands of years of experience in tempting and drawing people away from God and we are no match for him.
Paul urges his preacher boy, Timothy, to be patient in teaching others proper doctrine and Bible truth. Because many try to make Scripture say what they want by using their own reasoning and understanding and they become ensnared by the devil -- “And the servant of the Lord must not strive; but be gentle unto all men, apt to teach, patient, {25} In meekness instructing those that oppose themselves; if God peradventure will give them repentance to the acknowledging of the truth; {26} And that they may recover themselves out of the snare of the devil, who are taken captive by him at his will.” When we rely upon our own understanding we will end up ensnared by the devil at his will.
Some try to live the Christian life in their own strength and soon come to the realization they cannot and they fail and fall.
These bodies that we live in are weak by the curse upon sin from the Garden of Eden and we are foolish to think that we are able in our own strength to live out the Christian life. Paul tells us – “For if ye live after the flesh, ye shall die: but if ye through the Spirit do mortify the deeds of the body, ye shall live.” Paul says he can do all things through Christ and also he says that he will glory in his weakness that the power of Christ may rest upon him – “Most gladly therefore will I rather glory in my infirmities, that the power of Christ may rest upon me.” We live the Christian life by His power not our own and when we strive to live in our own power, wisdom, knowledge and understanding we are in danger of falling away from the faith.