Must Christians know God the Father, the Son, and the Holy Spirit as one God, and confess their faith in all of them? Yes. The reason is as follows.
God the Father, the Son, and the Holy Spirit all led the ministry of creation and gave life to mankind. But God the Father is the Father of the Holy Son. The Son fulfilled the ministries of the remission of sin—that is, He was baptized by John and crucified to save mankind from sin. The Holy Spirit took the task of bearing witness to those who believe that the baptism of Jesus and the blood of the Cross fulfilled the works of the atonement of mankind.
For us to become the perfect people of God, we need the faith that believes in God the Father, the Son, and the Holy Spirit in this way. It is because God the Father, the Son, and the Holy Spirit created the universe and us that we have come to exist in this world, and for God the Son to save sinners from their sins, the baptism that fulfilled the righteousness of God and the work of bloodshed on the Cross was required. Because Jesus was baptized by John and thereby took upon the sins of the world, He bore the punishment of these sins that we were supposed to bear and died on the Cross vicariously in our stead.
By doing so, those believers could finally be freed from all their sins. This truth had been prepared long before, and it is the core ministry of the gospel of the water and the Spirit. It is only when we apply this truth to us that Jesus Christ’s work of atonement finally become a work fulfilled for our own sake, and we can be saved from all our sins by believing.
If we had no knowledge of God the Father, the Son, and the Holy Spirit, then we would have been unable to know how the universe was created and who has given us life, and if there had not been God the Son, neither would we have been able to know the way of salvation—that is, how we could pass on our sins—nor what is the basis of our salvation from sin. But if there had been no Holy Spirit bearing witness, then no matter how great of a way of salvation has been prepared, this truth would have been just a pie in the sky, having nothing to do with us at all. Therefore, whenever we confess the faith of the Apostles’ Creed, we must think of God the Father, the Son, and the Holy Spirit who has created us and given us life, and we must stand firmly on our faith in the truth that these three independent Persons are one God for us.