1 John 5: 12-13
"And this is the record, that God hath given to us eternal life, and this life is in his Son. He that hath the Son hath life; and he that hath not the Son of God hath not life. These things have I written unto you that believe on the name of the Son of God; that ye may know that ye have eternal life, and that ye may believe on the name of the Son of God."
1 John 5: 18
"We know that whosoever is born of God sinneth not; but he that is begotten of God keepeth himself, and that wicked one toucheth him not."
As believers in Christ, we are "to attend to carefully" (Greek and Hebrew meaning of the word keepeth) not to live in willful rebellion against God, but to ensure that we keep ourselves from sin. When we sin or miss the mark of God's standard, we allow the enemy a foothold into our lives and this can be very destructive depending upon the trespass against God.
Walking humbly before the Lord in obedience and remaining in His will is the only way we can be confident that the enemy cannot touch us or afflict us. We have salvation through Christ our Lord because of our faith, but we have God's peace through our obedience to Him.