1 Corinthians 12:3 KJV
Wherefore I give you to understand, that no man speaking by the Spirit of God calleth Jesus accursed: and that no man can say that Jesus is the Lord, but by the Holy Ghost.
Keeping in mind that the context has to do with spiritual gifts and that this passage has a supporting text in 1 John, we find here two tests to prove a word is given by the Holy Spirit
No man who is filled with the Holy Ghost will curse Christ.
This is reasonably easy to implement. If a man or woman curses any aspect of Christ or His doctrine as given in the Word of God, they have not the Spirit regardless of what they may insist is true.
No man can say Jesus is Lord except that he is filled with the Holy Ghost.
This becomes much more challenging because
· Countless numbers have said those words having full knowledge and freely professing they do not believe it
· Multitudes more have said those words in feigned sincerity but have after proven not to be believers and
· Still more continue to say those words while espousing doctrines that are contrary to the message of God's Word
We must be misunderstanding that test.
"though a man may historically say all this, as the devils may, and hypocritically, as formal professors and foolish virgins do now, and will at the last day; and as all men then will by force, whether they will or not, confess that Jesus is Lord, who have not the Spirit of God; yet no man can call him his Lord, can appropriate him to himself truly and really, as his Lord, Saviour, and Redeemer, as David, Thomas, the Apostle Paul, and others have done; but by the Spirit; since such an appropriation includes spiritual knowledge of Christ, strong affection to him; faith of interest in him, an hearty profession of him, and sincere subjection to him; all which cannot be without the Spirit of God"
Simply put, a man may not be born again by the mere expression of the words but by a work of the Holy Ghost in his soul.
Modern soul winners need to more carefully consider what is their duty as witnesses for Jesus Christ. A man is not saved except that the Holy Spirit has worked. It is not ours to merely elicit a profession but to be tools of the Holy Spirit until He transforms the heart so that it must confess Jesus is Lord.
 1 John 4:1-3 KJV
Beloved, believe not every spirit, but try the spirits whether they are of God: because many false prophets are gone out into the world.
Hereby know ye the Spirit of God: Every spirit that confesseth that Jesus Christ is come in the flesh is of God:
And every spirit that confesseth not that Jesus Christ is come in the flesh is not of God: and this is that spirit of antichrist, whereof ye have heard that it should come; and even now already is it in the world.