Concerning those who died before Messiah’s First-Advent, where is their soul, their spirit?
Those who existed before Messiah found righteousness with Elohim just as those subsequent Messiah’s First-Advent; that is, righteousness (a right standing) with the Father was and is initiated by “faith;” that is, believing that God is true, God is real and that He will do exactly as He has promised (Hebrews 11).
Many men and women entered into covenant with the Father before Messiah; unfortunately, their sin had not received the acceptable atonement though that blood-atonement was first pictured in Genesis 3:21 and articulated subsequently in Leviticus 17:11, foreshadowed by the Levitical blood sacrifices and ultimately fulfilled by Messiah Jesus at Golgotha with the words “It is finished” (John 19:30).
Before Messiah’s blood atonement had manifest at Golgotha, those who died prior to that atonement, their spirit/soul was detained temporarily in Sheol (Hades-Greek)/Paradise (Luke 16) and while Messiah’s body laid in the tomb for three-days, Messiah, in Spirit (John 4:24), entered the region of Sheol-Paradise, preached the Gospel/liberty to them and subsequently escorted them into the Kingdom where nothing impure is permitted to exist (Ephesians 4:7-10; Revelation 21:27). These Old Testament saints had now received the imputed righteousness of Messiah over their existence by faith and were declared “not guilty” by covenant promise (2 Corinthians 5:21; Hebrews 8:12).
Disposition of the dead today?
Those who die subsequent Messiah’s atonement for sin having trusted in Jesus Christ as their Messiah by faith during their life constrained by Time and physics (John 3), they are immediately translated into the presence of our Lord as Sheol-Paradise is now unoccupied and irrelevant (2 Corinthians 5:8).
Only Sheol-Hades/Torments (Luke 16) remains relevant; this, for all unredeemed who die not in faith, not in covenant with the Father through faith in Jesus Christ, as these are awaiting the Great White Throne Judgment of the Condemned and will receive resurrected bodies of corruption and stand for adjudication before Jesus Christ immediately subsequent His Millennial Reign; these will be adjudicated guilty for their sin, their fleshly works of unrighteousness, and die the “second death”in the Lake of Fire in nihilism (Revelation 20:11-15).