So why are you imploring us to heed the theological advice of someone who is in hell?
Jefferson was correct in his affirmation of God as man's Creator and Endower of man's unalienable rights. The fact that according to God's Word, unless he acknowledged Jesus Christ as his Lord and Savior before he died he is spending eternity separated from God, does not change that.
Christ's Word recorded in Matthew, Chapter 11 gives indication that those who deny Him and do not repent will find their eternity separated from God (
in hell, as you indicate) more tolerable or less tolerable. This is just a guess, but knowing the mercy of God, there's a good chance that those who believe in and have publicly acknowledged God as man's Creator and Endower, will be among those finding their eternity in hell at least somewhat more tolerable than those who have not. Perhaps their torment will consist only of their eternal sorrow and regret.