You have yet to prove that a true child of God can reject his salvation. God will chastise His own - that is what Hebrews 12 teaches us. There is no Biblical authority for your opinion that a child of God could get so far backslidden that he would reject the Lord and his free gift of salvation. I do not believe God would ever let that believer get to that point. He will bring chastisement, and even death if the person persists in their rebellion - but He has promised NEVER to leave them nor forsake them - and if He sent them to Hell, He broke His promise...

So the only problem I see is your understanding of the faithfulness of God.

1 Corinthians 1:9 God is faithful, by whom ye were called unto the fellowship of his Son Jesus Christ our Lord.

1 Corinthians 10:13 There hath no temptation taken you but such as is common to man: but God is faithful, who will not suffer you to be tempted above that ye are able; but will with the temptation also make a way to escape, that ye may be able to bear it.

1 Thessalonians 5:23-24 And the very God of peace sanctify you wholly; and I pray God your whole spirit and soul and body be preserved blameless unto the coming of our Lord Jesus Christ. Faithful is he that calleth you, who also will do it.

2 Thessalonians 3:3 But the Lord is faithful, who shall stablish you, and keep you from evil.

1 Timothy 1:15 This is a faithful saying, and worthy of all acceptation, that Christ Jesus came into the world to save sinners; of whom I am chief.

2 Timothy 2:11-13 It is a faithful saying: For if we be dead with him, we shall also live with him: If we suffer, we shall also reign with him: if we deny him, he also will deny us: If we believe not, yet he abideth faithful: he cannot deny himself.

Hebrews 10:23 Let us hold fast the profession of our faith without wavering; (for he is faithful that promised

1 Peter 4:19 Wherefore let them that suffer according to the will of God commit the keeping of their souls to him in well doing, as unto a faithful Creator.

1 John 1:9 If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.

Revelation 19:11 And I saw heaven opened, and behold a white horse; and he that sat upon him was called Faithful and True, and in righteousness he doth judge and make war.

Hebrews 6:17-18 Wherein God, willing more abundantly to shew unto the heirs of promise the immutability of his counsel, confirmed it by an oath: That by two immutable things, in which it was impossible for God to lie, we might have a strong consolation, who have fled for refuge to lay hold upon the hope set before us: