You will find strong Bible believing Christians arguing on either side.  A view that settles the conflict within the scriptures is God knows who is saved and will endure to the end, but people can be mistaken about being saved and can turn away.  We say the Sun rises and sets, but that is only from our point of view.  It is the Earth that rotates, not the Sun going around the Earth.  Thus, From God's view, once a person is saved they stay saved, but from the human point of view, people can think they are save but fall away.  

Remember the parable of the wheat and the tares.

https://hermeneutics.stackexchange.com/questions/59533/understanding-the-parable-of-the-weeds-matthew-1324-30

The lost and the saved can look the same.  It is true that a person who attends church, goes through the motions, and is exposed to the truth, yet turns away, is worse off than a person who never knew about Christ.  

Senses of the word translated know in "know the Lord."

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The emphasis seems to be on people who understand what is required of them, but turning away rather than following.  

Example of scriptures that show God knows who will be saved:

> and all who dwell on earth will worship it, everyone whose name has not been written before the foundation of the world in the book of life of the Lamb who was slain.
(Rev. 13:8, ESV)

> 29 For those whom he foreknew he also predestined to be conformed to the image of his Son, in order that he might be the firstborn among many brothers. 30 And those whom he predestined he also called, and those whom he called he also justified, and those whom he justified he also glorified. 
(Rom. 8:29–30, ESV)

> 3 Blessed be the God and Father of our Lord Jesus Christ, who has blessed us in Christ with every spiritual blessing in the heavenly places, 4 even as he chose us in him before the foundation of the world, that we should be holy and blameless before him. In love 5 he predestined us for adoption to himself as sons through Jesus Christ, according to the purpose of his will, 6
(Eph. 1:3–6, ESV)

> 11 In him we have obtained an inheritance, having been predestined according to the purpose of him who works all things according to the counsel of his will, 
(Eph. 1:11, ESV)


> though they were not yet born and had done nothing either good or bad—in order that God’s purpose of election might continue, not because of works but because of him who calls— 12 she was told, “The older will serve the younger.” 13 As it is written, “Jacob I loved, but Esau I hated.” 
(Rom. 9:11–13, ESV)

> But God’s firm foundation stands, bearing this seal: “The Lord knows those who are his,” and, “Let everyone who names the name of the Lord depart from iniquity.” 
(2 Tim. 2:19, ESV)

>  And the LORD said to Moses, “When you go back to Egypt, see that you do before Pharaoh all the miracles that I have put in your power. But I will harden his heart, so that he will not let the people go.
(Exodus 4:21, ESV)

> All that the Father gives me will come to me, and whoever comes to me I will never cast out.
(John 6:37, ESV)

> No one can come to me unless the Father who sent me draws him.
(John 6:44, ESV)

> My sheep hear my voice, and I know them, and they follow me. 28 I give them eternal life, and they will never perish, and no one will snatch them out of my hand. 29 My Father, who has given them to me, is greater than all, and no one is able to snatch them out of the Father’s hand.
(John 10:27–29, ESV)

> They went out from us, but they were not of us; for if they had been of us, they would have continued with us. But they went out, that it might become plain that they all are not of us.
(1 John 2:19, ESV)



  [1]: https://i.sstatic.net/IejRz.png