JOEL - To me this means that we should trust in God and his eternal principles rather than in man and his changing earthly philosophies, theories and opinions. The Lord warns us against relying solely upon man's strength and wisdom. He said, "Cursed is he that putteth his trust in man, or maketh flesh his arm, or shall hearken unto the precepts of men, save their precepts shall be given by the power of the Holy Ghost." (2 Ne. 28:31.)
According to Elder Marvin J. Ashton , "One of the most common of all sins among worldly people is relying on and then boasting in the arm of flesh. This is a most serious evil. It is a sin born of pride, a sin that creates a frame of mind which keeps men from turning to the Lord and accepting his saving grace."
There's nothing wrong with gaining earthly knowledge and experience. That is one of the reasons why we are here. We must remember, however, that the revelations and knowledge that come from God are always true and always will be true. We can trust in Him to be right all the time. We should not let our wealth of earthly knowledge blind us with pride to the point that we no longer listen to Him and accept his word as the absolute truth.