1 John 3:1

The sentence opens with an imperative and it is unusual. See. John is not stating a fact; he is instructing the reader to look at something, the way you would take someone by the shoulder and turn them.

What he wants looked at is the size of it. The Greek phrase behind how great a love carries a note of foreignness — what country does this come from, what sort of thing is this. It is the reaction of someone encountering a species they cannot classify.

And the size is measured by the title, not by feeling: that we should be called children of God. Called, in this context, means named legally — the status conferred rather than the affection expressed. John then adds a short clause the older translations sometimes drop: and such we are. He is anticipating the objection. Not called as a courtesy. Called because it is the case.

Then the turn, and it is bracing. For this cause the world doesn't know us, because it didn't know him.

That is offered as evidence, not consolation. Being unrecognised is presented as consistent with the identity rather than a challenge to it. The people who missed who Jesus was are not likely to correctly identify his family, and John treats the misidentification as confirming the relationship rather than casting doubt on it.