I am the way, and the truth, and the life

Jesus Christ is not the Image of word alone, but the Image of invisible trinity God, that means in Jesus Christ we can see our Heavenly Father (I and the Father are one - John 10:30), and the Son (He who came down from heaven, that is, the Son of Man who is in heaven - John 3:13), and the Holy Spirit (if I do not go away, the Helper will not come to you - John 16:7).

Before going to the cross, In that crucial moment, Jesus Christ reveled about his divine trinity to his disciples that he is our Heavenly Father, Son, and the Holy Spirit - Let not your hearts be troubled. Believe in God; believe also in me. In my Father's house are many rooms. If it were not so, would I have told you that I go to prepare a place for you? And if I go and prepare a place for you, I will come again and will take you to myself, that where I am you may be also. And you know the way to where I am going. Thomas said to him, Lord, we do not know where you are going. How can we know the way? Jesus said to him, I am the way, and the truth, and the life. No one comes to the Father except through me - John 14:1-6

When Jesus said "Believe in God", He is referring our Heavenly Father, The Trinity God (Father, Word(Son) and Holy Spirit) - because there are three who are testifying in Heaven: the Father, the Word, and the Holy Spirit, and these three are one -  1 John 5:7

And when Jesus Said "Believe also in Me", He is referring the Son of man who is the image of Trinity God - (Holy Spirit, Father, and the Son) - and there are three who are testifying in the earth: the Spirit(Holy Spirit), and the water(Father), and the blood(Son) and the three are into the one(Jesus Christ) - 1 John 5:8

Now you know why Jesus Christ did not mention the Holy Spirit when he said "Believe in God; Believe also in Me".