Ecclesiastes 9:5 For the living know they will die; but the dead do not know anything,
Ecclesiastes 9:10 Whatever your hand finds to do, do it with all your might, for in the realm of the dead, where you are going, there is neither working nor planning nor knowledge nor wisdom.
Psalm 6:5 Among the dead no one proclaims your name. Who praises you from the grave?
Psalm 88:10 Do you show your wonders to the dead? Do their spirits rise up and praise you?
Psalm 115:17 It is not the dead who praise the LORD, those who go down to the place of silence;
Deuteronomy 18:10 Let no one be found among you who sacrifices their son or daughter in the fire, who practices divination or sorcery, interprets omens, engages in witchcraft, 11 or casts spells, or who is a medium or spiritist or who consults the dead.
1 Chronicles 10:13 So Saul died for his transgression which he committed against the LORD, even against the word of the LORD, which he kept not, and also for asking counsel of one that had a familiar spirit, to inquire of it; 14 And inquired not of the LORD: therefore he slew him, and turned the kingdom unto David the son of Jesse.
You have not shown one shred of evidence that those who have passed from this life are included in those we should have pray for us.
Some of these passages involve necromancy or “spiritualism,” which is NOT prayer. So those are irrelevant.
Some of the passages are about death FROM AN ENTIRELY EARTHLY POINT OF VIEW. They are not about life after death (pro or con) but about the FINALITY of death from our earthbound perspective.
Even granting that the rest of the passages are to be taken literally, there remains this question:
You believe that the Hebrew or Jewish belief at any given moment in the many centuries before Christ was the final, fully-developed truth?