It is true that all mankind is "condemned already" (John 3:18) as you quoted previously. It is true because all mankind has sinned and has become the children of the Devil.
1John 3:8 He that committeth sin is of the devil; for the devil (condemned) sinneth from the beginning. For this purpose the Son of God was manifested, that he might destroy the works of the devil. 9 Whosoever is born of God doth not commit sin (born again as a child of God); for his seed remaineth in him: and he cannot sin, because he is born of God. 10 In this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother.
Since all mankind are children of the Devil, all mankind will go to destruction and will perish. There are no exceptions to paying this penalty. At the end of the final age, mankind will cease to exist. But before mankind perishes, Christ has sworn that He will save all mankind and convert them into children of God. In other words, mankind will be born again and made into a new creation. The spiritual work of Christ to make this transition for all mankind is called conversion.
The believers are not condemned. Condemned already are the ones who do not believe. ( the believers in Christ are chastened of the Lord that they should not be condemned with the world.)..
John 3:18 He that believeth on him is
not condemned: but he that believeth
not is
condemned already, because he hath
not believed in the name of the only begotten Son of God.
1 Corinthians 11:32 But when we are judged, we are chastened of the Lord, that we should
not be
condemned with the world.
Children of the devil are those who do not love Jesus, and who do not believe that He proceeded and came forth from the Father.
Those of the devil cannot understand the word of Christ, and then being of their father the devil ( hearing his word) do the lusts of him. ( abiding in the one who was a murderer from the beginning)
Because Jesus tells the truth to the children of the devil, they DO NOT BELIEVE HIM.
Jesus again tells them ( the children of the devil) that they who are of Go hear Gods word, and although He says the truth to them, they have no reason to not believe Him, but that they do not hear HIs words BECAUSE THEY ARE NOT OF GOD.
The Son knows the Father, and if He said He does not know Him, He would be a liar like they are liars.
Those of the devil come again to Jesus, and Jesus tells them AGAIN, that the works He does in His Fathers name, bear WITNESS OF HIM.
But those of the devil do NOT BELIEVE, because THEY ARE NOT HIS SHEEP. as He SAID UNTO THEM ( not of God but are of their father the devil/if God was their Father they would love the Son of God sent forth.)
Jesus shows HIs sheep do hear HIs voice, He knows THEM, they follow Him...
John 8:42 Jesus said unto them, If God were your Father, ye would love me: for I proceeded forth and came from God; neither came I of myself, but he sent me.
43 Why do ye not understand my speech? even because ye cannot hear my word.
44 Ye are of your father the devil, and the lusts of your father ye will do. He was a murderer from the beginning, and abode not in the truth, because there is no truth in him. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father of it.
45 And because I tell you the truth, ye believe me not.
46 Which of you convinceth me of sin? And if I say the truth, why do ye not believe me?
47 He that is of God heareth God's words: ye therefore hear them not, because ye are not of God.
John 8:55 Yet ye have not known him; but I know him: and if I should say, I know him not, I shall be a
liar like unto
you: but I know him, and keep his saying.
John 10:25 Jesus answered them, I told you, and ye believed not: the works that I do in my Father's name, they bear witness of me.
26 But ye believe not, because ye are not of my sheep, as I said unto you.
27 My sheep hear my voice, and I know them, and they follow me:
Since not all are children of the devil, here is MORE DISTINCTION, for belief. ( belief was already given to the sheep to believe in their Shepherd sent to them/the works He FINISHED, bear WITNESS OF HIM.)
Satan, the devil, continues ( in the antichrist spirit) with all LYING.
Strong delusion for them to BELIEVE A LIE. ( the sheep believe THE TRUTH.)
To RECEIVE THE LOVE OF THE TRUTH, is to be saved. ( believe in your heart God raised Christ from the dead and you will be SAVED. Romans 10:10.) Jesus is the door, for the sheep to go in and out find pasture and BE SAVED.
The DAMNED, do not BELIEVE THE TRUTH.
Remembering that the devil WAS A MURDERER FROM THE BEGINNING, abode not in the truth, the beloved of the Lord, ( HIs sheep He knows) are CHOSEN FROM THE BEGINNING, to salvation, through sanctification of the spirit, and BELIEF OF THE TRUTH. ( because Jesus tells the truth the children of the devil DO NOT BELIEVE/ in Him risen to be SAVED.)...
John 10:9 I am the door: by me if any man enter in, he shall be saved, and shall go in and out, and
find pasture.
2 Thessalonians 2:9 Even him, whose coming is after the working of Satan with all power and signs and lying wonders,
10 And with all deceivableness of unrighteousness in them that perish; because they received not the love of the truth, that they might be saved.
11 And for this cause God shall send them strong delusion, that they should believe a lie:
12 That they all might be damned who believed not the truth, but had pleasure in unrighteousness.
13 But we are bound to give thanks alway to God for you, brethren beloved of the Lord, because God hath from the beginning chosen you to salvation through sanctification of the Spirit and belief of the truth:
14 Whereunto he called you by our gospel, to the obtaining of the glory of our Lord Jesus Christ.
The devil we understand murdered/sinned FROM THE BEGINNING.
The seed of the wicked one are not sown by God. ( sown by the devil) but the children of the kingdom are sown by God. ( His seed remains in him.) that is THOSE WHO ARE BORN OF GOD.
In this is MANIFESTED the CHILDREN OF GOD, and the CHILDEEN OF THE DEVIL, ( the children of the devil do not believe in their heart unto righteousness of Christ rising, to be saved. Romans 10:9-10.) they do not do righteousness, they do NOT LOVE THEIR BROTHER. ( tares gathered to all be burned/cast into the lake of fire with their father the devil.)
The righteous ( His sheep who hear His voice/the truth, unlike the children of the devil/goats who do not believe the truth told and FULFILLED by Christ.) shine forth in the kingdom of their Father. (the devil is cast into the fire, second death, anyone NOT FOUND written in the book of life was cast into the same lake of fire. ( the Lamb was slain from the foundation of the world, HIs fellow sheep believe He was raised by God the Father, and all whose names are NOT WRITTEN IN THE LAMBS BOOK OF LIFE, worship the beast.)..
Matthew 13:37 He answered and said unto them, He that soweth the good seed is the Son of man;
Matthew 13:38 The field is the world; the good
seed are the children of the kingdom; but the tares are the children of the
wicked one;
Matthew 13:39 The enemy that sowed them is the devil; the harvest is the end of the world; and the reapers are the angels.
Matthew 13:42 And shall cast them into a furnace of fire: there shall be wailing and gnashing of teeth.
43 Then shall the righteous shine forth as the sun in the kingdom of their Father. Who hath ears to hear, let him hear.
Revelation 13:8 And all that dwell upon the earth shall worship him, whose names are not written in the
book of
life of the
Lamb slain from the foundation of the world.
Revelation 20:10 And the devil that deceived them was cast into the lake of fire and brimstone, where the beast and the false prophet are, and shall be tormented day and night for ever and ever.
Revelation 20:14 And death and hell were cast into the lake of fire. This is the second death.
15 And whosoever was not found written in the book of life was cast into the lake of fire.
1 John 3:8 He that committeth sin is of the devil; for the devil sinneth from the beginning. For this purpose the Son of God was manifested, that he might destroy the works of the devil.
9 Whosoever is born of God doth not commit sin; for his seed remaineth in him: and he cannot sin, because he is born of God.
10 In this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother.