It was the apostle Peter that tells us these words stated in I Peter 5:8 that says, "Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour." An adversary is an opponent that can fight against us for many different reasons. It can be a person that dislikes someone and will go to great lengths to cause them harm in one way or another. Peter tells us that Satan is our adversary that walks about like a roaring lion seeking whom he may devour. In order for Satan to devour a person that certain person would have to be vulnerable to his attacks, which means that person would be void of Satan's wiles and tactics. This is why the prophet Hosea tells us these words saying in Hosea 4:6 that says, "My people are destroyed for lack of knowledge: because thou hast rejected knowledge, I will also reject thee, that thou shalt be no priest to me: seeing thou hast forgotten the law of thy God, I will also forget thy children." Not knowing what Gods word has to say about the ways and wiles of our adversary the devil this will leave us prone to his ability to devour us. To know what Gods word has to say about anything that we are told to believe or do and for anybody not to believe or do what it says is down right rebellion against God. This is true, because Gods word tell us that if anyone knows to do good and does it not, then to that person it becomes sin against God. Satan has many caught up in this deception causing them to count what Gods word says to be insignificant or that God overlooks some things he says, but God means what he says and says what he means. If a person believes that some things that God has said in his word can be overlooked and believed or obeyed, because it's not really that important, then that person is guilty of willfully sinning against God, which is a sin that has a dire warning against. To sin willfully against God is done by knowing what his word says about something and go right on and do it or not do it anyway.
As an example, Gods word tells us not to let sin reign in our mortal body, but if we allow sin to reign in our mortal body and do nothing about it, then we have willfully sinned against God. It was the apostle Peter that tells us these words in 2 Peter 2:21 that says, "For it had been better for them not to have known the way of righteousness, than, after they have known it, to turn from the holy commandment delivered unto them." Satan, who is the adversary of Gods people, has caused many to think and believe that every word of God is not all that important, but that certain things can be overlooked. Take as an example how many people are saying that it's alright to tell their children that there is a Santa Claus that brings their gifts to them at Christmas. That is a lie of the devil, but yet millions of people will overlook that and tell their children there is a Santa Claus knowing full well that Santa Claus is nothing more or less than an idol that does not exist. What about you friend, are you living by "every word that has proceeded from the mouth of God" or are you in disobedience somewhere or another thinking that God is not all that intolerable? If so then Satan is sifting you like wheat and will eventually devour and destroy you.