After pastoring for forty years I can state unequivocally that the most common cause of spiritual weakness in a Christian (or a church) is a failure to recognize the flesh in its disguise of religious zeal. Like Peter flashing a sword in Gethsemane the fleshly Christian thinks he is doing God's will and fighting God's battles for him.
Perhaps one of the commonest expressions of this misguided zeal is the practice of "binding Satan" before Christian ministry is attempted. The Word of God gives no justification for this practice. None of the apostles utilized this approach and no Scripture commands Christians to practice it. It is an exta-biblical performance, arising from the desire of the flesh to look committed and powerful in the service of God. Christians are told to "resist the devil" but never to bind him. Resisting the devil is done by putting on the whole armor of God, as Paul describes it in Ephesians 6. The "binding and loosing" mentioned in Matthew 18:18 refers to the agreement in prayer of believers in line with the promises of God revealed in his Word.
Another form of this same error is to ascribe the manifestations of the flesh to the work of demons, which then are ostensibly "cast out" of an individual through a "deliverance ministry." But Galatians 5:19-21 clearly tell us that lust, hatred, discord, jealousy, rage, envy, sexual orgies, and the like are not the work of demons but of the flesh. It is impossible to "cast out" the flesh during this lifetime---rather it is to be subdued by recognizing its evil character, refusing to yield mind or body to its impulses, and turning immediately to Jesus for the supply of his strength and purity, as Romans 6:13 so clearly outlines.
It is plainly the work of pastors and teachers to help Christians identify the flesh in themselves, by means of the Word of God, and to follow the pattern the Word describes to keep the flesh in subjection to the spirit and the individual free to live as the Lord has already made provision to do.
It is for freedom that Christ has set us free. Stand firm then, and do not let yourselves be burdened again by a yoke of slavery. (Galatians. 5:1).