Who is redeemed and who is lost is ultimately determined by God and not the opinions of mortal men. God has mercy on whom he will and God also hardened whom he will according to his word in line with the age and doctrines that apply to that time period.
Ro 9:13 As it is written, Jacob have I loved, but Esau have I hated. 14 ¶ What shall we say then? Is there unrighteousness with God? God forbid. 15 For he saith to Moses, I will have mercy on whom I will have mercy, and I will have compassion on whom I will have compassion. 16 So then it is not of him that willeth, nor of him that runneth, but of God that sheweth mercy. In what men call the church age from the the cross until the translation of the church every born again Christian that places their trust in Jesus Christ cannot lose their salvation they have eternal security.
Ro 8:31 ¶ What shall we then say to these things? If God be for us, who can be against us? 32 He that spared not his own Son, but delivered him up for us all, how shall he not with him also freely give us all things?33 Who shall lay any thing to the charge of God's elect? It is God that justifieth. 34 Who is he that condemneth? It is Christ that died, yea rather, that is risen again, who is even at the right hand of God, who also maketh intercession for us. 35 Who shall separate us from the love of Christ? shall tribulation, or distress, or persecution, or famine, or nakedness, or peril, or sword? 36 As it is written, For thy sake we are killed all the day long; we are accounted as sheep for the slaughter.37 Nay, in all these things we are more than conquerors through him that loved us. 38 For I am persuaded, that neither death, nor life, nor angels, nor principalities, nor powers, nor things present, nor things to come, 39 Nor height, nor depth, nor any other creature, shall be able to separate us from the love of God, which is in Christ Jesus our Lord. Under the law men did not have eternal security and they could lose their soul. My opinion in reading the text would be that Manasseh repented and he was a soul that was redeemed by Gods grace and mercy. A study of the word also reveals that sometimes there are exceptions to rules as it also appears that David had eternal security in an age where men could lose their soul.
Isa 55:3 Incline your ear, and come unto me: hear, and your soul shall live; and I will make an everlasting covenant with you, even the sure mercies of David. Remember that exceptions always prove the rule!
