NO, HE TOLD US HOW TO TELL.
Matthew 7:16 (NKJV)
16 You will know them by their [spiritual] fruits. Do men gather grapes from thornbushes or figs from thistles?
Matthew 7:20-23 (NKJV)
20 Therefore by their fruits you will know them.
21 "Not everyone who says to Me, 'Lord, Lord,' shall enter the kingdom of heaven, but he who does the will of My Father in heaven.
22 Many will say to Me in that day, 'Lord, Lord, have we not prophesied in Your name, cast out demons in Your name, and done many wonders in Your name?'
23 And then I will declare to them, 'I never knew you [that expression means they were not Born Again]; depart from Me, you who practice lawlessness!'
Galatians 5:22-23 (NKJV)
22 But the fruit of the Spirit is [Agape Godly] love, joy, peace, longsuffering, kindness, goodness, faithfulness,
23 gentleness, self-control. Against such there is no law.
1 John 3:16-19 (NKJV)
16 By this we know [Agape Godly] love, because He laid down His life for us. And we also ought to lay down our lives for the brethren.
17 But whoever has this world's goods, and sees his brother in need, and shuts up his heart from him, how does the [Agape Godly] love of God abide in him?
18 My little children, let us not [agapaō Godly] love in word or in tongue, but in deed and in truth.
19 And by this we know that we are of the truth, and shall assure our hearts before Him.