If Father is the Only True God, how can Father, Son and Holy Spirit be God?
Those sentences which are colored in orange are from Maharishi Dayananda Saraswati book Satyarth Prakash (The Light of Truth) and those which are colored in black are Jerry Thomas’s response.
"The only true God." (17:3.)C. When He is the only true God, it is absurd for the Christians, to talk about three Gods. (The Father, the Son and the Holy Ghost).
Answer: In the Old Testament, Yahweh God had acted many times to let know the people that there is only one True God, that is Yahweh, and the gods of others nations are false.
It was not to declare the numerical oneness of Yahweh but to declare that there is no God besides Yahweh who is triune in nature.
LORD Jesus Christ here is speaking in the Jewish context of Only True God which means that only Yahweh is the only true God and not the gods of other nations.
For example, in Deuteronomy 4, Prophet Moses begins by saying:
Deuteronomy 4:3-4 “Your eyes have seen what the LORD did at Baal Peor; for the LORD your God has destroyed from among you all the men who followed Baal of Peor. But you who held fast to the LORD your God are alive today, every one of you.”
Deuteronomy 4:35-39 To you it was shown, that you might know that the LORD Himself is God; there is none other besides Him. Out of heaven He let you hear His voice, that He might instruct you; on earth He showed you His great fire, and you heard His words out of the midst of the fire. And because He loved your fathers, therefore He chose their descendants after them; and He brought you out of Egypt with His Presence, with His mighty power, driving out from before you nations greater and mightier than you, to bring you in, to give you their land as an inheritance, as it is this day. Therefore know this day, and consider it in your heart, that the LORD Himself is God in heaven above and on the earth beneath; there is no other.
2 Kings 5:15 And he returned to the man of God, he and all his aides, and came and stood before him; and he said, "Indeed, now I know that there is no God in all the earth, except in Israel; now therefore, please take a gift from your servant."
In this sense, the Triune Yahweh God is the only true God.
Now let us quote the very passage to see if LORD Jesus Christ is the One True God.
John 17: 1-8 “Jesus spoke these words, lifted up His eyes to heaven, and said: "Father, the hour has come. Glorify Your Son, that Your Son also may glorify You as You have given Him authority over all flesh, that He should give eternal life to as many as You have given Him. And this is eternal life, that they may know You, the only true God, and Jesus Christ whom You have sent. I have glorified You on the earth. I have finished the work which You have given Me to do. And now, O Father, glorify Me together with Yourself, with the glory which I had with You before the world was. I have manifested Your name to the men whom You have given Me out of the world. They were Yours, You gave them to Me, and they have kept Your word. Now they have known that all things which You have given Me are from You. For I have given to them the words which You have given Me; and they have received them, and have known surely that I came forth from You; and they have believed that You sent Me.
(a) LORD Jesus Christ has authority over all flesh- In other words, God the Father Shares authority with LORD Jesus Christ.
(b) LORD Jesus Christ gives eternal life to as many as Father as given Him.
(c) LORD Jesus Christ had Glory with the Father.
(d) LORD Jesus Christ was with the Father before the world began.
In other words, LORD Jesus Christ existed with the Father before the world began shared God’s glory and authority and gives eternal life.
There is no denial by LORD Jesus Christ that He is God. Therefore this passage should be understood in the Old Testament context which would mean that there is no God except Yahweh.