The firstborn is primarily the oldest son of a father (rather than the firstborn of the mother), the beginning of the father’s generative power (De 21:17); also, the initial male offspring of animals, at times designated as “firstlings.”​—Ge 4:4.

From earliest times the firstborn son held an honored position in the family and was the one who succeeded to the headship of the household. He inherited a double portion of the father’s property. (De 21:17) Reuben was seated by Joseph at a meal according to his right as firstborn. (Ge 43:33) But the Bible does not always honor the firstborn by listing sons according to birth. The first place is often given to the most prominent or faithful of the sons rather than to the firstborn.​—Ge 6:10; 1Ch 1:28; compare Ge 11:26, 32; 12:4; see BIRTHRIGHT; INHERITANCE.

The firstborn came into considerable prominence at the time that Jehovah delivered his people from slavery in Egypt. Among the Egyptians, the firstborn were dedicated as sacred to the sun-god Amon-Ra, the supposed preserver of all the firstborn. The tenth plague that Jehovah brought upon the Egyptians served to discredit this god and showed up his inability to protect the firstborn. By obeying God’s instructions concerning the slaying of a lamb and the splashing of its blood on the doorposts and upper part of the doorway of their houses, the Israelites did not lose their firstborn in death, whereas all the firstborn of the Egyptians, of both man and beast, were slain. (Ex 12:21-23, 28, 29) Evidently the firstborn son of each household is meant in most cases and not the head of the household, even though he may have been a firstborn. Pharaoh himself was probably a firstborn and yet his life was not taken. However, it may be that not every Egyptian household had a literal firstborn son (the married couple being childless or the firstborn son having already died), and in view of the statement at Exodus 12:30, “there was not a house where there was not one dead,” the destruction could have included the chief one in the house occupying the position of firstborn.

Since the firstborn sons among the Israelites were those in line to become the heads of the various households, they represented the entire nation. Jehovah, in fact, referred to the whole nation as his “firstborn,” it being his firstborn nation because of the Abrahamic covenant. (Ex 4:22) In view of his having preserved their lives, Jehovah commanded that “every male firstborn that opens each womb among the sons of Israel, among men and beasts,” be sanctified to him. (Ex 13:2) Thus, the firstborn sons were devoted to God.

Later Jehovah took the male Levites, evidently aside from the 300 Levite firstborn (compare Nu 3:21, 22, 27, 28, 33, 34 with 3:39), in place of the firstborn sons of Israel, from those one month old and upward. A ransom price of five shekels ($11) had to be paid to Aaron and his sons for each of the 273 in excess of the Levites. Also, Jehovah took the domestic animals of the Levites in place of the firstborn domestic animals of the other  tribes. (Nu 3:40-48) From that time forward, a firstborn son was to be presented to Jehovah at the tabernacle or temple after the period of the mother’s uncleanness and be redeemed by the payment of the estimated value for those from a month up to five years old, “five silver shekels by the shekel of the holy place.”​—Le 12:1-3; 27:6; Nu 18:15, 16.

The firstborn males of clean animals, such as the bull, lamb, or goat, were not to be redeemed. Such a bull was not to be worked, nor was the lamb to be sheared. Instead, they were to be presented to Jehovah as a sacrifice at the tabernacle or temple on the eighth day after birth. (Ex 22:30; Nu 18:17; De 15:19, 20) If, however, the animal had a bad defect, it was not to be sacrificed to Jehovah but was to be eaten at one’s place of dwelling.​—De 15:21-23.

The firstborn of an ass, an unclean animal, could not be presented as a sacrifice and, therefore, was to be redeemed, or bought back, by substituting a sheep in its place. Otherwise, its neck was to be broken, since it belonged to Jehovah and was not to be used by man. (Ex 13:12, 13; 34:19, 20) However, Leviticus 27:27 reads: “If it is among the unclean beasts and he must redeem it according to the estimated value, he must then give a fifth of it in addition to it. But if it should not be bought back, it must then be sold according to the estimated value.” Some commentators view this text as a modification of the regulation concerning the redeeming of an ass. Apparently, though, Leviticus 27:27 deals with a different matter. Instead of referring to an unclean animal, such as an ass, the words “if it is among the unclean beasts” may denote an animal that was unclean in the sense of being unfit for sacrifice because of being blemished.

Why does Jehovah refer to “David my servant” as firstborn, when David was not a firstborn son?

In Psalm 89 Jehovah refers to “David my servant” and reviews the covenant for the kingdom that was made with him. In the midst of this is the statement: “I myself shall place him as firstborn, the most high of the kings of the earth.” (Ps 89:20, 27) David was not a firstborn son. (1Ch 2:13-15) So it seems that Jehovah was referring prophetically to the one foreshadowed by David, God’s own “firstborn” Son in heaven upon whom He confers kingship more exalted than that of any human ruler.​—Compare Eze 34:24, where Messiah is spoken of as “my servant David.”

Jesus Christ is shown to be “the firstborn of all creation” as well as “the firstborn from the dead”​—not merely most distinguished in relation to those created or those resurrected but the first one actually created and the first raised from the dead to endless life. (Col 1:15, 18; Re 1:5; 3:14) On earth he was the firstborn child of Mary and was presented at the temple in accordance with Jehovah’s law. (Lu 2:7, 22, 23) The apostle Paul speaks of the followers of Jesus Christ who have been enrolled in the heavens as “the congregation of the firstborn,” the first ones accepted by God as sons on the basis of their faith in Jesus’ sacrifice and the first of Christ’s followers to be resurrected with no need to die again.​—Heb 12:23.

At Job 18:13 the expression “firstborn of death” is used to denote the most deadly of diseases.