John draws a clear distinction here between those who are of God and those who are not.  He begins the chapter by declaring that many false prophets are gone out into the world, and he tells us that these prophets are of the world.  Consequently they speak of the world and the world hears them.  In other words, their ministry is a worldly ministry that is received and embraced by worldly people.  But in contrast to this, John says, "We are of God: he that knoweth God heareth us; he that is not of God heareth us not.   Hereby know we the spirit of truth, and the spirit of error."  Using this test the followers of Christ still today may determine those who are motivated by the spirit of truth and those who are motivated by the spirit of error.

A person who is "not of God" simply cannot hear the "joyful sound" of that gospel which was preached by Christ and His apostles, and which is still preached today by those that God has put into the ministry (See I Tim. 1:12).  Some of those to whom Christ Himself preached were "not of God," and to them He said, "Why do ye not understand my speech? Even because ye cannot hear my word.  Ye are of your father the devil, and the lusts of your father ye will do" (John 8:43-44).  Spiritual hearing requires spiritual discernment, or understanding, and natural men (those who are yet spiritually unborn) have no such discernment (I Cor. 2:14). It requires an "ear to hear" (See for instance Rev. 2:7,11,17,29, etc.), and without that spiritual "ear" there can be no hearing of spiritual things.  The things of the spirit of God are hidden from the wise and prudent and revealed unto babes (See Matt. 11:25).  And, it is given unto some to know the mysteries of the kingdom of heaven, but to others it is not given (See Matt. 13:11).

The apostle Paul said, "We speak the wisdom of God in a mystery, even the hidden wisdom, which God ordained before the world unto our glory; which none of the princes of this world knew…" (I Cor. 2:7).  If everyone had the ability to receive the gospel, such scriptures would have no place. ---Elder Ralph Harris