Let’s talk “spirit” and “soul” first.
Now “spirit” can refer to the Holy Spirit, an attitude (“a spirit of anger”), and in either Greek or Hebrew, the wind and the breath.
It’s easy to see how both languages might use the same word for wind and breath. In fact, in English, we do the same thing when we say, “I’m winded” or “I got my second wind.” “Wind” means breath in that context.
But in the Bible, when used of a human, “spirit” means something like “spark of life” in Hebrew and biblical Greek. To die is to “give up the spirit,” not meaning that our soul floats up heaven, but life leaves the body.
(Gen 2:7 ESV) then the LORD God formed the man of dust from the ground and breathed into his nostrils the breath [spirit = nephach] of life, and the man became a living creature [soul = nephesh].
Regarding the meaning of “spirit” —
From the standpoint of theology, the Bible is slow to isolate the spirit aspect of man’s makeup. In Genesis spirit occurs only twice with reference to humans: the pharaoh’s spirit was troubled after his dreams (Gn 41:8) and Jacob’s spirit revived when he saw the carts Joseph sent from Egypt (45:27). Exodus adds little, speaking only of the Israelites’ anguish of spirit (6:9), of a spirit of wisdom imparted by God for designing the priests’ garments (28:3), and of persons with a willing spirit supplying gold for the tabernacle (35:21).
… But it is in the poetic books, Job, Psalms, Proverbs, and Ecclesiastes, that we begin to get the more metaphysical and psychological uses of spirit. Here life, personhood, and immortality come into focus.
A clear case of the parallel (synonymous) use of soul and spirit (as in Jb 7:11; Is 26:9, etc.) is in Mary’s Magnificat. She says, “My soul magnifies the Lord, and my spirit has rejoiced in God my Savior” (Lk 1:46, 47, NKJV). Rather than divide the two as “parts,” some have suggested man has a spirit, he is a soul. (First Jn 4:1, however, unless referring to external influences, seems to employ spirit as synonymous with person.) Usually spirit indicates the vitalizing, energizing, empowering agent. In John 3:5–8; Romans 8:3–16, Galatians 4:21–5:26, etc., the flesh versus spirit distinction is between man’s will and power, doing what he chooses apart from God, as against the life, will, and power given by God’s Spirit, enabling us to do his will. Similarly, in 2 Kings 2:9–15, the spirit of Elijah is said to rest upon Elisha.
Loss of the spirit spells death (Lk 23:46; Jas 2:26), while eternal spiritual life is generated through Christ’s spirit-word (Jn 6:63).
Walter A. Elwell and Barry J. Beitzel, “Spirit,” Baker Encyclopedia of the Bible, 1988, 1991–1992.
Just so, “soul” can refer to a person (five souls died yesterday) or a person’s inner nature (I love you from the depths of my soul).
The Greek philosopher Plato (4th century B.C.) perceived the soul as the eternal element in man: whereas the body perishes at death, the soul is indestructible. At death the soul enters another body; if it has been wicked in this life, it may be sent into an inferior human being, or even an animal or bird. By means of transmigration from one body to another, the soul is eventually purged of evil. In the early centuries of the Christian era, Gnosticism also taught that the body was the prison house of the soul. Redemption comes to those initiated into the Gnostic secrets, leading to the release of the soul from the body.
Biblical thought about the soul is different. In the OT the soul signifies that which is vital to man in the broadest sense. The Hebrew and Greek words for soul often can be translated as “life”; occasionally they can be used for the life of creatures (Gen 1:20; Lv 11:10). “Soul for soul” means “life for life” (Ex 21:23). Blood is said to be the seat of life, for when blood is shed death ensues (Gn 9:4–6; Lv 17:11, 14; Dt 12:23). In legal writings a soul means the person concerned in a particular law (e.g., Lv 4:2; 5:1, 2, 4, 15). When people were counted, they were counted as souls, that is, persons (Ex 1:5; Dt 10:22).
In a narrower sense the soul denotes man in his varied emotions and inner powers. Man is called to love God with all his heart and soul (Dt 13:3). Within the soul lies the desire for food (12:20, 21), the lust of the flesh (Jer 2:24), and the thirst for murder and revenge (Ps 27:12). The soul is said to weep (Jb 30:16; Ps 119:28), and to be exercised in patience (Jb 6:11). Knowledge and understanding (Ps 139:14), thought (1 Sm 20:3), love (1 Sm 18:1), and memory (Lam 3:20) all originate in the soul. Here the soul comes close to what today would be called the self, one’s person, personality, or ego.
There is no suggestion in the OT of the transmigration of the soul as an immaterial, immortal entity. Man is a unity of body and soul—terms which describe not so much two separate entities in man as the one man from different standpoints. Hence, in the description of man’s creation in Genesis 2:7, the phrase “a living soul” (KJV) is better translated as “a living being.” The thought is not that man became a “soul,” for clearly he had a body. The use of the word in the original draws attention to the vital aspect of man as “a living being.” The Hebrew view of the unity of man may help to explain why man in the OT had only a shadowy view of life after death, for it would be difficult to conceive how man could exist without a body (Pss 16:10; 49:15; 88:3–12). Where hope of an after-life exists, it is not because of the intrinsic character of the soul itself (as in Plato). It is grounded in confidence in the God who has power over death and the belief that communion with him cannot be broken even by death (Ex 3:6; 32:39; 1 Sm 2:6; Jb 19:25, 26; Pss 16:10, 11; 73:24, 25; Is 25:8; 26:19; Dn 12:2; Hos 6:1–3; 13:14).
In the NT the word for soul (psychē) has a range of meanings similar to that of the OT. Often it is synonymous with life itself. Followers of Jesus are said to have risked their lives for his sake (Acts 15:26; cf. Jn 13:37; Rom 16:4; Phil 2:30). As the Son of Man, Jesus came not to be served, but to serve and to give his life as a ransom for many (Mt 20:28; Mk 10:45). As the Good Shepherd, he lays down his life for the sheep (Jn 10:14, 17, 18). In Luke 14:26 the condition of discipleship is to hate one’s soul, that is, to be willing to deny oneself to the point of losing one’s life for Christ’s sake (cf. Lk 9:23; Rv 12:11). In Luke 12:19 the rich man addresses his soul, that is, himself. But the soul can indicate the essential self of a man with its desire for life and well-being.
Frequently “soul” can mean “person” (Acts 2:43; 3:23; 7:14; 27:22; Rom 2:9; 13:1; 1 Pt 3:20). The expression “every living soul” (Rv 16:3 KJV; cf. 8:9) reflects the vital aspect of living beings (cf. Gn 2:7). In his teaching on the resurrection Paul contrasts the merely physical aspect of the soul with the resurrection body. “Thus it is written, ‘The first man Adam became a living being’; the last Adam [Christ] became a life-giving spirit” (1 Cor 15:45). In the following verses Paul goes on to contrast the resurrection body with the natural body. It is clear that Paul is talking neither about the immortality of the soul nor of the resuscitation of corpses to the state in which they were at death. The resurrection body will be a new kind of body. “Just as we have borne the image of the man of dust, we shall also bear the image of the man of heaven” (v 49).
As in the OT the soul can denote not only the vital aspect of the person on the physical level, but it can also connote one’s emotional energies. It denotes man himself, the seat of his emotions, man in his inmost being. Jesus could speak of his soul being crushed (Mt 26:38; Mk 14:34; cf. Ps 42:6). In Matthew 11:29 Jesus promises rest to the souls of those who come to him. Here as elsewhere “soul” denotes the essential person (cf. Lk 2:35; 2 Cor 1:23; 2 Thes 2:8; 3 Jn 2).
Walter A. Elwell and Barry J. Beitzel, “Soul,” Baker Encyclopedia of the Bible, 1988, 1987–1988.
So a fertilized ovum doesn’t become a human when it receives a soul — ensoulment, as some say. It’s a soul when it becomes human. God doesn’t give souls to babies, born or unborn. Humans are souls.
(I’m really not entirely sure what the implications of this truth are for the abortion debate. I just know that we’d do better to debate in scriptural terms rather than pagan Platonic terms.)