This term “gathered to his people” is used throughout all Old Testament referring to the death of the Patriarchs.

Gen 25:8 Then Abraham gave up the ghost, and died in a good old age, an old man, and full [of years]; and was gathered to his people.

Gen 25:17 and these [are] the years of the life of Ishmael, an hundred and thirty and seven years: and he gave up the ghost and died; and was gathered unto his people.

Gen 35:29 And Isaac gave up the ghost, and died, and was gathered unto his people, [being] old and full of days: and his sons Esau and Jacob buried him.

Jacob said in Gen.49:29 "I am to be gathered to my people."

Gen 49:33 And when Jacob had made an end of commanding his sons, he gathered up his feet into the bed, and yielded up the ghost, and was gathered unto his people.

Num 20:24 Aaron shall be gathered unto his people: for he shall not enter into the land

Deu 32:50 And die in the mount whither thou goest up, and be gathered unto thy people; as Aaron thy brother died in mount Hor, and was gathered unto his people:

David said that when his son died (2 Sam. 12:28) I will go to him he will not come to me.

Thus in the Old Testament, death is not an extinction, or annihilation of the person, but a departure from the material world into the spirit world where all the generations are still living.

These spirits are referred to as “Rephaim” in the Old Testament Hebrew.

Jewish Virtual Library gives two meanings for the word, Rephaim. (Heb. ).

~ “ The first is as a gentilic (e.g., Gen. 14:5; 15:20; Deut. 2:11) referring to a people distinguished by their enormous stature.  (Deut. 3:11) ...(ll Sam. 21:16, 18, 20).  (e.g., II Sam. 21:16, 18, 20;l Chron. 20:8).  Septuagint's renderings gigantes and titanes as well as for gabbaré of the Peshitta and gibbarayya of the Targums. The Genesis Apocryphon (21 :28) on the other hand prefers the noncommital repha'ayya.

In its second use Rephaim designates "shades" or "spirits" and serves as a poetic synonym for metim ( _;; Isa. 26:14; Ps. 88:11). “

ATS Bible Dictionary also affirms the same notion.

“The Hebrew word is used in two distinct significations.

1. REPHAIM is used to comprehend all the gigantic races of the Canaanites, of whom there were several families. There were Rephaim beyond Jordan, at Ashtaroth Karnaim, in the time of Abraham, Genesis 14:5; also some in the time of Moses. Og king of Bashan was of the Rephaim. In the time of Joshua, some of their descendants dwelt in the land of Canaan, Joshua 12:4 17:15, and we hear of them in David's time, in the city of Gath, 1 Chronicles 20:4-6. The giant Goliath and others were the remains of the Rephaim, or of the kindred family of Anakim. Their magnitude and strength are often spoken of in Scripture. They appear to have excelled in violence and crime, and hence are monuments of divine justice.

2. REPHAIM, the shades or spirits of the departed, dwelling in Sheol or Hades, generally rendered in our version, "the dead" ("dead things," Job 26:5); Psalm 88:10; Proverbs 2:18; 21:16, etc.

Here are the biblical verses:

Job 26:5 The departed spirits [ rephaim] tremble under the waters and their inhabitants.

Ps. 88:10 Wilt Thou perform wonders for the dead? Will the departed spirits [rephaim] rise and praise Thee?

Prov. 2:18 For the adulteress' house sinks down to the departed spirits [rephaim]

Prov 9:18 The thief does not know that the departed spirits [rephaim] are there, that her guests are in the depths of Sheol.

Prov 21 :16 A man who wanders from the way of understanding will rest in the assembly of the departed spirits [rephaim]

Isa 26:19 the earth will give birth to the departed spirits. [rephaim]

Isa. 14:9-11 the King of Babylon: Isa 14:9-11 "Sheol from beneath is excited over you to meet you when you come; It arouses for you the spirits of the dead [rephaim], all the leaders of the earth;  "They will all respond and say to you, ‘Even you have been made weak as we, You have become like us. ‘Your pomp and the music of your harps Have been brought down to Sheol.

This concept is again found in the Jewish after death mourning period rituals known as Shiva rituals. Shiva (Hebrew: ) (literally "seven") is the week-long mourning period in Judaism for first-degree relatives: father, mother, son, daughter, brother, sister, and spouse. The ritual is referred to as "sitting shiva." Immediately after burial, people assume the halakhic status of "avel" (Hebrew: ‘nu ; "mourner"). This state lasts for seven days, during which family members traditionally gather in one home (preferably the home of the deceased) and receive visitors. A tear is made on the garment of the mourner over the heart if the deceased is a parent, or over the right side of the chest for other relatives. This tearing of the clothing is referred to as keriyah (lit. "tearing"). The mourner recites the blessing describing G-d as "the true Judge," an acceptance of God's taking of the life of a relative.

In Jewish tradition, a flame symbolized the soul of man reaching ever upward. This is suggested by the verse in Proverbs 20:27, "The soul of man is the lamp of the Lord." By lighting a candle and keeping it burning throughout the Shiva period, it is believed that the soul of the departed is aided in its journey heavenward.

Today, a memorial or Shiva candle is kept burning for the duration of Shiva. There are some who will continue to keep one burning throughout the entire first year of mourning.