We have to “know the only true God and the one he sent” if we want everlasting life....why only two....why don’t we need to know the third equal party? (John 17:3)
You simply do not understand (are in ignorance, not knowing of) what Jhn. 17:3 actually states.
John 17:2-3:
Joh 17:2 As thou hast given him power over all flesh, that he should give eternal life to as many as thou hast given him.
Joh 17:3 And this is life eternal, that they might know thee the only true God, and Jesus Christ, whom thou hast sent.
Joh 17:3 αυτη δε εστιν η αιωνιος ζωη ινα γινωσκωσιν σε τον μονον αληθινον θεον και ον απεστειλας ιησουν χριστον
Jhn. 17:3, Jesus, as the eternal Son, is praying (in the Holy Ghost/ Spirit) to His eternal Father, in Heaven, and it is inspired by the eternal Holy Ghost / Spirit, since Jesus is praying and it is written (Jhn. 17:8,14,17 KJB) as scripture (2 Tim. 3:16-17; 2 Pet. 1:21 KJB, &c.). Jesus is also the "Christ" or "anointed" by the Holy Ghost / Spirit in the text. All Three Persons / Beings are mentioned in the text, though the Holy Ghost less obvious, as the Holy Ghost is more silent, as the 'camera-man' behind the scenes, as it were, inspiring the prayer of Jesus, and the words to be recorded as scripture for us to read in our own day / time.
1. "the only true God" - "τον μονον αληθινον θεον" = the Person / Being of the Father, the word "alethinon" meaning 'true' or 'underived', referring to His own nature (see vs 2 in relation). The Father's eternal nature is His own, and is derived from no one.
"and" (in addition to)
2. "Jesus [JEHOVAH is salvation] Christ [Anointed by the Holy Ghost / Spirit of the Father]. The Son's nature stems from the Father's nature, which is why the Son is "ton monogene", or "the only-begotten" (the only one with the same nature), the only Son with the Nature of the Father. Only in that way are their natures differing. In this way is the Son the 'second-self' (a descriptive, yet a differing Person / Being) to that of the Father, as Eve was to Adam in type.
3. The "Christ" is a reference to the "anointing" of Jesus [JEHOVAH is salvation] by the Holy Ghost / Spirit, see Luke. 4:18; Isa. 61:1 KJB, and the prayer of Jesus is being inspired by the Holy Ghost / Spirit in the first place, & the text itself, is inspired of the Holy Ghost / Spirit, and thus in every single text of scripture which is of God is inspired of the Holy Ghost, or witnessed by the Holy Ghost (such as satan's words in the beginning, or words of enemeis of God, &c).
JEHOVAH Elohiym - Godhead:
(1.) The Person / Being of the Father (Mat. 6:9; Luk. 11:2 KJB), JEHOVAH (“the LORD”, Gen. 19:24b; Zec. 3:2b KJB), the “Ancient of Days” (Dan. 7:9,13,22 KJB), “the only true God” (Jhn. 17:3 KJB; “τον μονον αληθινον θεον”), “God” (Psa. 45:7b.; Heb. 1:9b.; Jhn. 1:1b KJB, “τον θεον”), speaking to the Son:
(A.) Revelation 4:11 KJB - Thou art worthy, O Lord, to receive glory and honour and power: for thou hast created all things, and for thy pleasure they are and were created.
(B.) Revelation 10:6 KJB - And sware by him that liveth for ever and ever, who created heaven, and the things that therein are, and the earth, and the things that therein are, and the sea, and the things which are therein, that there should be time no longer:
(C). Genesis 1:6 KJB - And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters.
(2.) The Person / Being of the Son, Jesus JEHOVAH ((H3444; H3068) “ישׁועתה ליהוה”; Gen. 49:18; Exo. 14:13; 2 Chr. 20:17; Jon. 2:10; Psa. 119:174 HOT) or JEHOVAH Immanuel ((Psa. 46:7,11) Psa. 46:8,12 HOT, (H3068; H5973; H430), “יהוה ... עמנו... אלהי”), “the LORD” (Gen. 19:24a.; Zec. 3:2a.; Heb. 1:10; Psa. 102:12,25-27; Heb. 13:4-8), “the son of man” (Dan. 7:13), “the only begotten” (Jhn. 1:14,18, 3:16,18; Heb. 11:17; 1 Jhn. 4:9, is basically monogene (μονογενῆ; Jhn. 3:16; Heb. 11:17; 1 Jhn. 4:9) or monogenes (μονογενὴς; Jhn. 1:18) or monogenous (μονογενοῦς; Jhn. 1:14, 3:18)), “the Lord Jesus Christ, the Son of the Father” (2 Jhn. 1:3; Κυρίου Ἰησοῦ Χριστοῦ τοῦ υἱοῦ τοῦ πατρός), “the express image of his (God, The Father’s) person” (Heb. 1:3; χαρακτὴρ τῆς ὑποστάσεως αὐτοῦ), being Himself also “God” (Jhn. 1:1c., “θεος ην ο λογος”; Jhn. 1:14,18, 3:16,18; Heb. 11:17; 1 Jhn. 4:9; Psa. 47:5a.; Heb. 1:8,9a.), even “O God” (Heb. 1:9, “ο θεος”), and the “son of man” (Dan. 7:13), the “fellow” (Zec. 13:7), who acted, “made” all things (Jhn. 1:1-3; Eph. 3:9; Col. 1:16; Heb. 1:1-3), on behalf of the Father’s will (Pro. 8:22-36; Jhn. 5:30, 6:38), though, a father in His own right (Isa. 9:6; Heb. 2:13; Isa. 8:16,18; Jhn. 13:33), and yet also the perfect Son (Num. 19:2; “without spot, wherein is no blemish, and upon which never came yoke”), the “Angel (Messenger)” (Mal. 3:1b) “of the LORD (Father)” (Zec. 3:1); “Michael” (Dan. 10:13,21, 12:1; 1 Thes. 4:16; Jud. 1:9; Rev. 12:7), the great “I am” (Jhn. 8:58; ἐγὼ εἰμί), see also Jhn. 4:26, 6:20,35,41,48,51, 8:12,18,24,28,58, 9:5, 10:7,9,11,14, 11:25, 14:6, 15:1,5, 18:5,6,8, 13:19:
(A.) John 1:1 KJB - In the beginning was the Word, and the Word was with God, and the Word was God.
John 1:2 KJB - The same was in the beginning with God.
John 1:3 KJB - All things were made by him; and without him was not any thing made that was made.
(B.) Ephesians 3:9 KJB - And to make all men see what is the fellowship of the mystery, which from the beginning of the world hath been hid in God, who created all things by Jesus Christ:
(C.) Colossians 1:16 KJB - For by him were all things created, that are in heaven, and that are in earth, visible and invisible, whether they be thrones, or dominions, or principalities, or powers: all things were created by him, and for him:
(D.) Hebrews 1:1 KJB - God, who at sundry times and in divers manners spake in time past unto the fathers by the prophets,
Hebrews 1:2 KJB - Hath in these last days spoken unto us by his Son, whom he hath appointed heir of all things, by whom also he made the worlds;
(E.) Genesis 1:7 KJB - And God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament: and it was so.
(3.) The Person / Being of the Holy Ghost / Spirit, the “another Comforter” (Jhn. 14:16 KJB), the “Spirit of truth.” (Jhn. 14:17 KJB), “Comforter ... the Holy Ghost” (Jhn. 14:26 KJB), the “LORD” (Zec. 3:2c KJB), and a father in His own right (Mat. 1:18; Luk. 1:35; 1 Pet. 1:23; Jhn. 1:13, 3:3-8; 1 Jhn. 3:9, 4:7, 5:1,4,18 KJB), yet differing than the Father or the Son (Isa. 48:16; Jhn. 14:26 KJB):
(A.) Job 33:4 KJB - The Spirit of God hath made me, and the breath of the Almighty hath given me life.
(B.) Genesis 1:2 KJB - And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters.
(C.) Genesis 1:31 KJB - And God saw every thing that he had made, and, behold, it was very good. And the evening and the morning were the sixth day.