He wanted to reveal of himself so that we can enter in a meaningful relationship with him. That does not mean he is three persons and nothing else. That would be Tri-theism, since several persons are always distinct in human experience. And on top of it, these three persons are said to be ONE God. God being the Trinity means that He is community in Himself.
Love always needs at least a subject and and object.
And true love is always giving and taking. Then He would at 'some time' not have been love. And he says He is unchangeable, eternally the same God. There is so much more that could be said here. But I think, I should close this mathematical-theological exploration at this point.