Unsaved Persons can be very religious.

Unsaved people can be quite religious.
These natural men devoid of the Spirit can still make claims to religious ideas.
World religions show the religions of demon-worshipping natural men.
Sometimes some of these religious persons even show up on religious message boards.
They offer ides and opinions without any scriptural support.
Without the Spirit, they cannot perceive Divine truth.

• Young's Literal Translation
  Chapter Parallel
  Jude 1:12 (YLT) These are in your love-feasts craggy rocks; feasting together with you, without fear shepherding themselves; clouds without water, by winds carried about; trees autumnal, without fruit, twice dead, rooted up;
  
  
• Wycliffe
  Chapter Parallel
  Jude 1:12 (WYC) These be in their meats, feasting together to filth [These be in their meats filths, or defoulings, feasting together], without dread feeding themselves. These be clouds without water, that be borne about of winds; harvest trees without fruit, twice dead, drawn up by the root;
  
  
• Weymouth New Testament
  Chapter Parallel
  Jude 1:12 (WNT) These men--sunken rocks! --are those who share the pleasure of your love-feasts, unrestrained by fear while caring only for themselves; clouds without water, driven away by the winds; trees that cast their fruit, barren, doubly dead, uprooted;
  
  
• World English Bible
  Chapter Parallel
  Jude 1:12 (WEB) These are hidden rocky reefs in your love feasts when they feast with you, shepherds who without fear feed themselves; clouds without water, carried along by winds; autumn leaves without fruit, twice dead, plucked up by the roots;
  

How do you deal with unsaved religious professors?
What is the best and most loving thing to do for them?

 

Yes, The law is the perfect tool to help them discover the true condition of their hearts.

Here is a demon-infested man who was sitting in good standing in this synagogue. No one suspected him evidently.
lk4;
31 And came down to Capernaum, a city of Galilee, and taught them on the sabbath days.

32 And they were astonished at his doctrine: for his word was with power.

33 And in the synagogue, there was a man, which had a spirit of an unclean devil, and cried out with a loud voice,

34 Saying, Let us alone; what have we to do with thee, thou Jesus of Nazareth? art thou come to destroy us? I know thee who thou art; the Holy One of God.

35 And Jesus rebuked him, saying, Hold thy peace, and come out of him. And when the devil had thrown him in the midst, he came out of him, and hurt him not.

36 And they were all amazed, and spake among themselves, saying, What a word is this! for with authority and power he commandeth the unclean spirits, and they come out.

37 And the fame of him went out into every place of the country round about.

 

Perhaps his conscience is not yet seared. keep up the steady witness you have begun with him, with questions that might be as seeds for him to mull over. It will work towards his damnation, or salvation;
2cor2:
14 Now thanks be unto God, which always causeth us to triumph in Christ, and maketh manifest the savour of his knowledge by us in every place.

15 For we are unto God a sweet savour of Christ, in them that are saved, and in them that perish:

16 To the one we are the savour of death unto death; and to the other the savour of life unto life. And who is sufficient for these things?

17 For we are not as many, which corrupt the word of God: but as of sincerity, but as of God, in the sight of God speak we in Christ.

 

One thing that unsaved religious professors do, is attempt to explain away biblical teaching as the teachings of men.
Any excuse will do if someone seeks to avoid facing the truth of God.
Unsaved men want to de-throne God and put self upon the throne.
This is not possible, however they are in unbelief as those described in psalm 10...they do not believe they will answer to God for it.
Psalm 10 King James Version (KJV)
10 Why standest thou afar off, O Lord? why hidest thou thyself in times of trouble?

2 The wicked in his pride doth persecute the poor: let them be taken in the devices that they have imagined.

3 For the wicked boasteth of his heart's desire, and blesseth the covetous, whom the Lord abhorreth.

4 The wicked, through the pride of his countenance, will not seek after God: God is not in all his thoughts.

5 His ways are always grievous; thy judgments are far above out of his sight: as for all his enemies, he puffeth at them.

6 He hath said in his heart, I shall not be moved: for I shall never be in adversity.

7 His mouth is full of cursing and deceit and fraud: under his tongue is mischief and vanity.

8 He sitteth in the lurking places of the villages: in the secret places doth he murder the innocent: his eyes are privily set against the poor.

9 He lieth in wait secretly as a lion in his den: he lieth in wait to catch the poor: he doth catch the poor, when he draweth him into his net.

10 He croucheth, and humbleth himself, that the poor may fall by his strong ones.

11 He hath said in his heart, God hath forgotten: he hideth his face; he will never see it.

12 Arise, O Lord; O God, lift up thine hand: forget not the humble.

13 Wherefore doth the wicked contemn God? he hath said in his heart, Thou wilt not require it.

14 Thou hast seen it; for thou beholdest mischief and spite, to requite it with thy hand: the poor committeth himself unto thee; thou art the helper of the fatherless.

15 Break thou the arm of the wicked and the evil man: seek out his wickedness till thou find none.

16 The Lord is King for ever and ever: the heathen are perished out of his land.

17 Lord, thou hast heard the desire of the humble: thou wilt prepare their heart, thou wilt cause thine ear to hear:

18 To judge the fatherless and the oppressed, that the man of the earth may no more oppress.

 

Unsaved persons devoid of biblical truth often create their own version of God, and in reality their own gospel.
It seems much easier to do that.
Instead of learning mainstream teaching they invent teaching that fits their emotional feeling of how they think things should be, rather than what is declared.

This conduct is seen in scripture;
Judges 17:6
In those days there was no king in Israel, but every man did that which was right in his own eyes.

isa29:
10 For the Lord hath poured out upon you the spirit of deep sleep, and hath closed your eyes: the prophets and your rulers, the seers hath he covered.

11 And the vision of all is become unto you as the words of a book that is sealed, which men deliver to one that is learned, saying, Read this, I pray thee: and he saith, I cannot; for it is sealed:

12 And the book is delivered to him that is not learned, saying, Read this, I pray thee: and he saith, I am not learned.

13 Wherefore the Lord said, Forasmuch as this people draw near me with their mouth, and with their lips do honour me, but have removed their heart far from me, and their fear toward me is taught by the precept of men:

14 Therefore, behold, I will proceed to do a marvellous work among this people, even a marvellous work and a wonder: for the wisdom of their wise men shall perish, and the understanding of their prudent men shall be hid.

15 Woe unto them that seek deep to hide their counsel from the Lord, and their works are in the dark, and they say, Who seeth us? and who knoweth us?

 

Let us resolve to talk more to believers about the Bible when we meet them. Alas, the conversation of Christians, when they do meet, is often sadly unprofitable! How many frivolous, and trifling, and uncharitable things are said!

 

Unsaved religious persons can many times think that they can know what other people are thinking. They ascribe evil motives and invent false reports about people they want to be critical of.

You would think that a grown person would not give themselves to such a putrid task. Unsaved persons are perishing without the hope of the gospel, and yet such persons have a fixed agenda with their thoughts and ideas central, rather than Jesus.
Here are a couple of examples of this sinful conduct.

3 And he entered again into the synagogue; and there was a man there which had a withered hand.

2 And they watched him, whether he would heal him on the sabbath day; that they might accuse him.

3 And he saith unto the man which had the withered hand, Stand forth.

4 And he saith unto them, Is it lawful to do good on the sabbath days, or to do evil? to save life, or to kill? But they held their peace.


3jn:
9 I wrote unto the church: but Diotrephes, who loveth to have the preeminence among them, receiveth us not.

10 Wherefore, if I come, I will remember his deeds which he doeth, prating against us with malicious words: and not content therewith, neither doth he himself receive the brethren, and forbiddeth them that would, and casteth them out of the church.

11 Beloved, follow not that which is evil, but that which is good. He that doeth good is of God: but he that doeth evil hath not seen God.

 

These truths are interrelated. They spill over into all areas of life. Natural men who pretend to be believers can put on a facade, a religious veneer.
The flesh cannot sustain it however, and the sin oozes out.

 

Yes, listening is an important skill to develop in trying to come along side a person in need.