How can the formulation of Christian teaching one nature in three person and three persons in one nature be reasonable?

Answer: Refer carefully once again to Chap. 5, particularly 5, IV.

When the one God is love (mutual self-giving, see 1 Jn 4:7-21), then the three persons in one are simultaneously the intersections between which the rhythm of love is consummated: Giving – Receiving – Returning (Please note that Person in this context has a different significance to that of a person with a human personality as an independent in itself-centred reality). With that, all three Persons are one and the same love in three beings that are indispensable so that God can even be love at all, and – moreover… the highest selfless love. The one God is community, which means, he is the one loving game that takes place between the three Persons: Love, to be loved, to love with others.

In 1 Jn 1:3 it says: We declare to you what we have seen and heard so that you also may have the fellowship with us; and truly your fellowship with the Father and with his Son Jesus Christ.

Everything points to unity. And here, also, it is not about a commonplace unity, but a unity that receives its model from the three-in-one God. It is a unity that is realised in its variety and a variety that is moving towards unity. It is communio (communion, community).

The unity that the whole world strives for, the desire for unanimity, harmony and peace that is in every one of us, yes, the globalisation, interconnection and universal communication, which all technology, media and culture aim for, have something in common with the Holy Trinity, with Christian belief in the one God in three Persons. More precisely: There should be equivalence, a similarity between the two. This confirms this thesis once more: What God is, communio, is what we can and must become. He is the beginning of all and the target of all reality. In him, we are, we live and we move in him.

When God works on us, he always works as the one, three-in-one, God.