The Fourth Gospel is unique in the perspective it gives on the Trinity. From the outset of the gospel, John makes it clear that Jesus is fully God:
In the beginning was the Word, and the Word was with God, and the Word was God...The Word became flesh and made his dwelling among us.
It is hard for our finite minds to comprehend that Jesus is God AND He is separate from His Father AND that God is One. But those are the clear implications of Jesus' own words. Here are some of the highlights:
"I and the Father are one." —John 10:30
"...whatever the Father does the Son also does." —John 5:19
"If you know me, you will know my Father also."—John 14:7
"Anyone who has seen me has seen the Father."— John 14:9
"The words I say to you are not just my own. Rather, it is the Father, living in me, who is doing his work." — John 14:10
"Father, I have brought you glory on earth by completing the work you gave me to do. And now, Father, glorify me in your presence with the glory I had with you before the world began."— John 17:4-5
Because Jesus is fully divine ("the word was God") and fully human ("the word became flesh"), His sacrifice on the cross is able to atone for all sin. He is able to take His life up again. And able to give life to those who believe.
As Jesus prepares to return to the Father, He comforts the disciples by telling them about the Holy Spirit, who is also divine and characterized by truth. This third person in the Godhead will continue the ministry of Christ after He is gone.
"I will ask the Father, and he will give you another Counselor to be with you forever--the Spirit of truth....you know him, for he lives with you and will be in you. —John 14:15-18
"But the Counselor, the Holy Spirit, whom the Father will send in my name, will teach you all things and will remind you of everything I have said to you."—John 14:26
"When the Counselor comes, whom I will send to you from the Father, the Spirit of truth who goes out from the Father, he will testify about me. —John 15:26
But when he, the Spirit of truth, comes, he will guide you into all truth. He will not speak on his own; he will speak only what he hears, and he will tell you what is yet to come. He will bring glory to me by taking from what is mine and making it known to you. All that belongs to the Father is mine. That is why I said the Spirit will take from what is mine and make it known to you.—John 16:13-15
In this gospel, we get a glimpse of the somewhat puzzling reality of a triune God. One thing is clear, each person in the Trinity is involved with revealing truth and communing with believers. We are triply blessed to be in relationship with the Lord who loves us and seeks to have us know Him.