Brahman is defined to be ultimate subject. That is, it is the true form of the knower, and the knower cannot be separate from what is known.
For example, in Vyavahaarika Satya, we can talk of “my body,” “my mind,” and so on. But then, who is this I who’s body and mind exists? At that level, when you realize who “you” are, according to Vedanta, there is no “my” anything.
That is, you say you have a hand because you identify as being trapped in a limited body, and you see that your hand is something that you can lose. You never say you are the hand, because you know that the hand is separate from your self. Likewise, your vitality, mind and intellect are all separate from your essence, where you are one alone without another.
So when you say to “know Brahman,” it is not you knowing Brahman, another, but you knowing yourself. That is why “realize Brahman” is a more meaningful word.
It is kind of like remembering the person you are. But even in that, you are remembering the person you used to be as opposed to who you are now, or in other words, you are recollecting the past. But Brahman is your eternal self that never changes.