We are of God. He who knows God hears us; he who is not of God does not hear us. By this we know the spirit of truth and the spirit of error.
“We are of God” Those who are born again [through the Holy Spirit] in Christ.
“He who knows God hears us” A true believer of Jesus Christ will listen to the message that comes from the Word of God. While others, who are devoid of the Holy Spirit, when the message of Scripture is spoken to them, they will reject it.
Every messenger that bears a spiritual message is directed by either the Holy Spirit or by a demonic spirit. The Bible is the revealer of which spirit is leading the person.
Scripture quotation is from the NKJV