We straight away infer it because that is how the original author meant us to infer it. It is how they wrote when they wanted you to see something important. There are countless ways to tell the story without using “I am.” They chose their words very carefully. They tell you what is important without saying it so artlessly as … “And Jesus invoked Tetragramaton.”
How do you decide when “I am” is used to refer to the Divine Name among all the times “I am” stated in John (NIV):
John 1:21
They asked him, “Then who are you? Are you Elijah?” He said, “I am not.” “Are you the Prophet?” He answered, “No.”
John 1:23
John replied in the words of Isaiah the prophet, "I am the voice of one calling in the desert, ‘Make straight the way for the Lord.’ "
John 1:27
He is the one who comes after me, the thongs of whose sandals I am not worthy to untie."
John 3:28
You yourselves can testify that I said, ‘I am not the Christ but am sent ahead of him.’
John 4:9
The Samaritan woman said to him, “You are a Jew and I am a Samaritan woman. How can you ask me for a drink?” (For Jews do not associate with Samaritans. )
John 5:7
“Sir,” the invalid replied, “I have no one to help me into the pool when the water is stirred. While I am trying to get in, someone else goes down ahead of me.”
John 5:36
"I have testimony weightier than that of John. For the very work that the Father has given me to finish, and which I am doing, testifies that the Father has sent me.
John 6:35
Then Jesus declared, "I am the bread of life. He who comes to me will never go hungry, and he who believes in me will never be thirsty.
John 6:41
At this the Jews began to grumble about him because he said, “I am the bread that came down from heaven.”
John 6:48
I am the bread of life.
John 6:51
I am the living bread that came down from heaven. If anyone eats of this bread, he will live forever. This bread is my flesh, which I will give for the life of the world."
John 7:8
You go to the Feast. I am not yet going up to this Feast, because for me the right time has not yet come."
John 7:28
Then Jesus, still teaching in the temple courts, cried out, "Yes, you know me, and you know where I am from. I am not here on my own, but he who sent me is true. You do not know him,
John 7:29
but I know him because I am from him and he sent me."
John 7:33
Jesus said, "I am with you for only a short time, and then I go to the one who sent me.
John 7:34
You will look for me, but you will not find me; and where I am, you cannot come."
John 7:36
What did he mean when he said, ‘You will look for me, but you will not find me,’ and ‘Where I am, you cannot come’?"
John 8:12
The Validity of Jesus’ Testimony ] When Jesus spoke again to the people, he said, “I am the light of the world. Whoever follows me will never walk in darkness, but will have the light of life.”
John 8:14
Jesus answered, "Even if I testify on my own behalf, my testimony is valid, for I know where I came from and where I am going. But you have no idea where I come from or where I am going.
John 8:16
But if I do judge, my decisions are right, because I am not alone. I stand with the Father, who sent me.
John 8:18
I am one who testifies for myself; my other witness is the Father, who sent me."
John 8:21
Once more Jesus said to them, “I am going away, and you will look for me, and you will die in your sin. Where I go, you cannot come.”
John 8:23
But he continued, "You are from below; I am from above. You are of this world; I am not of this world.
John 8:24
I told you that you would die in your sins; if you do not believe that I am the one I claim to be, you will indeed die in your sins."
John 8:28
So Jesus said, "When you have lifted up the Son of Man, then you will know that I am the one I claim to be and that I do nothing on my own but speak just what the Father has taught me.
John 8:38
I am telling you what I have seen in the Father’s presence, and you do what you have heard from your father. "
John 8:46
Can any of you prove me guilty of sin? If I am telling the truth, why don’t you believe me?
John 8:49
“I am not possessed by a demon,” said Jesus, "but I honor my Father and you dishonor me.
John 8:50
I am not seeking glory for myself; but there is one who seeks it, and he is the judge.
John 8:58
“I tell you the truth,” Jesus answered, “before Abraham was born, I am!”
John 9:5
While I am in the world, I am the light of the world."
John 9:9
Some claimed that he was. Others said, “No, he only looks like him.” But he himself insisted, “I am the man.”
CONT.