The important point is not whether we can understand the Trinity, even with the help of illustrations, but whether we will believe what the Bible has to say about the Father, Son and Holy Spirit, and about their relationship to each other. What the Bible says may be summarized in the following five propositions:
1. There is but one living and true God who exists in three persons: God the Father, God the Son and God the Holy Spirit. We have already looked at this truth in general. We will see it more fully when I talk about the full deity of the Son and Holy Spirit in books two and three in this volume. Here we note a plurality within the Godhead that is suggested even in the pages of the Old Testament, before the Incarnation of the Lord Jesus Christ or the coming of the Holy Spirit upon all God's people. The plurality may be seen, in the first instance, in those passages in which God speaks about himself in the plural. One example is Genesis 1:26. "Then God said, 'Let us make man in our image, after our likeness.' " Another is Genesis 11:7. "Come, let us go down, and there confuse their language." A third is Isaiah 6:8. "And I heard the voice of the Lord saying, 'Whom shall I send, and who will go for us?' " In other passages a heavenly being termed "the angel of the Lord" is, on the one hand identified with God and yet, on the other hand, is also distinguished from him. Thus, we read: "The angel of the LORD found her [Hagar] by a spring of water in the wilderness. . . . The angel of the LORD said to her, 'I will so greatly multiply your descendants that they cannot be numbered for multitude.' . . . So she called the name of the LORD who spoke to her, 'Thou art a God of seeing' " (Gen. 16:7, 10, 13). An even stranger case is the appearance of the three angels to Abraham and Lot. The angels are sometimes spoken of as three and sometimes as one. Moreover, when they speak, it is the Lord who, we are told, speaks to Lot and Abraham (Gen. 18).
A final, startling passage is Proverbs 30:4. The prophet Agur is speaking about the nature of Almighty God, confessing his ignorance of him. "Who has ascended to heaven and come down? Who has gathered the wind in his fists? Who has wrapped up the waters in a garment? Who has established all the ends of the earth?" Then comes, "What is his name, and what is his son's name? Surely you know!" In that day the prophet knew only the Father's name, the name Jehovah. Today we know that his Son's name is the Lord Jesus Christ.
2. The Lord Jesus Christ is fully divine, being the second person of the Godhead who became man. This, of course, is where the crux of debate on the Trinity is to be found; those who dislike the doctrine dislike it primarily because they are unwilling to give such an exalted position to "the man" Jesus.
Such reluctance is seen first in the teachings of Arius of Alexandria (died A.D. 336). Sabellius, mentioned earlier, tended to merge the persons of the Trinity, so that Father, Son and Holy Spirit were only temporary manifestations of the one God, assumed for the purposes of our redemption. Arius, whose main work was done just after Sabellius, went to the other extreme. He divided the persons of the Trinity so the Son and the Spirit became less than God the Father. According to Arius, the Son and Spirit were beings willed into existence by God for the purpose of acting as his agents in redemption. Thus, they were not eternal (as God is), and they were not fully divine. Arius used the word divine to describe them in some lesser sense than when applying it to the Father. In more recent centuries the same error has been espoused by Unitarians and by some modern cults.
But it is a great error. For if Christ is not fully divine, then our salvation is neither accomplished nor assured. No being less than God himself, however exalted, is able to bear the full punishment of the world's sin.
The deity of the Lord Jesus Christ is taught in many crucial passages. We read "In the beginning was the Word, and the Word was with God, and the Word was God. He was in the beginning with God" (Jn. 1:1-2). That John 1:1-2 speaks of the Lord Jesus Christ is clear from John 1:14, in which we are told that the "Word" of verse 1 "became flesh and dwelt among us." Similarly, Paul writes, "Have this mind among yourselves, which you have in Christ Jesus, who, though he was in the form of God, did not count equality with God a thing to be grasped, but emptied himself, taking the form of a servant, being born in the likeness of men. And being found in human form he humbled himself and became obedient unto death, even death on a cross" (Phil. 2:5-8). The words "did not count equality with God a thing to be grasped, but emptied himself" do not mean that Jesus ceased to be fully God in the Incarnation, as some have maintained, but only that he temporarily laid aside his divine glory and dignity in order to live among us. We remember that it was during the days of his life here that Jesus said, "I and the Father are one" (Jn. 10:30), and "He who has seen me has seen the Father" (Jn. 14:9).
3. The Holy Spirit is fully divine. It is the Lord Jesus Christ who most clearly teaches the nature of the Holy Spirit. In the Gospel of John, Jesus compares the ministry of the coming Holy Spirit to his own ministry. "And I will pray the Father, and he will give you another Counselor, to be with you for ever, even the Spirit of truth, whom the world cannot receive, because it neither sees him nor knows him" (Jn. 14:16-17). This understanding of the Holy Spirit is supported by the fact that distinctly divine attributes are ascribed to him: everlastingness (Heb. 9:14), omnipresence (Ps. 139:7-10), omniscience (1 Cor. 2:10-11), omnipotence (Lk. 1:35) and others.
4. While each is fully divine, the three persons of the Godhead are related to each other in a way that implies some differences. Thus, it is usually said in Scripture that the Father (not the Spirit) sent the Son into the world (Mk. 9:37; Mt. 10:40; Gal. 4:4), but that both the Father and the Son send the Spirit (Jn. 14:26; 15:26; 16:7). We don't know fully what such a description of relationships within the Trinity means. But usually it is said that the Son is subject to the Father, for the Father sent him, and that the Spirit is subject to both the Father and the Son, for he is sent into the world by both the Son and Father. However, we must remember that when we speak of subjection we do not mean inequality. Although related to each other in these ways, the members of the Godhead are nevertheless "the same in substance, equal in power and glory," as the Westminster Shorter Catechism says (Q. 6).
5. In the work of God the members of the Godhead work together. It is common among Christians to divide the work of God among the three persons, applying the work of creation to the Father, the work of redemption to the Son and the work of sanctification to the Holy Spirit. A more correct way of speaking is to say that each member of the Trinity cooperates in each work.
One example is the work of creation. It is said of God the Father, "Of old thou didst lay the foundation of the earth, and the heavens are the work of thy hands" (Ps. 102:25); and "In the beginning God created the heavens and the earth" (Gen. 1:1). It is written of the Son, "For in him all things were created, in heaven and on earth, visible and invisible" (Col. 1:16); and "All things were made through him, and without him was not anything made that was made" (Jn. 1:3). It is written of the Holy Spirit, "The spirit of God has made me" (Job 33:4). In the same way, the Incarnation is shown to have been accomplished by the three persons of the Godhead working in unity, though only the Son became flesh (Lk. 1:35). At the baptism of the Lord all three were also present: the Son came up out of the water, the Spirit descended in the appearance of a dove and the voice of the Father was heard from heaven declaring, "This is my beloved Son, with whom I am well pleased" (Mt. 3:16-17). All three persons were present in the atonement, as Hebrews 9:14 declares. "Christ... through the eternal Spirit offered himself without blemish to God." The resurrection of Christ is likewise attributed sometimes to the Father (Acts 2:32), sometimes to the Son (Jn. 10:17-18) and sometimes to the Holy Spirit (Rom. 1:4).
We are not surprised, therefore, that our salvation as a whole is also attributed to each of the three persons: chosen and destined by God the Father and sanctified by the Spirit for obedience to Jesus Christ and for sprinkling with his blood" (1 Pet. 1:2). Nor are we surprised that we are sent forth into all the world to "make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit" (Mt. 28:19).
Again let me note, although we can say meaningful things about the Trinity (on the basis of God's revelation of them), the Trinity is still unfathomable. We should be humble before the Trinity. Someone once asked Daniel Webster, the orator, how a man of his intellect could believe in the Trinity. "How can a man of your mental caliber believe that three equals one?" his assailant chided. Webster replied, "I do not pretend fully to understand the arithmetic of heaven now." The doctrine of the Trinity does not mean that three equals one, of course, and Webster knew that. It means rather that God is three in one sense and one in another. But Webster's reply nevertheless showed a proper degree of creature humility. We believe the doctrine of the Trinity, not because we understand it, but because the Bible teaches it and because the Spirit himself witnesses within our heart that it is so.