By Westminster Confession, Chapter 2, Paragraph 3
3-In the unity of the Godhead there be three persons, of one substance, power, and eternity: God the Father, God the Son, and God the Holy Ghost:[62] the Father is of none, neither begotten, nor proceeding; the Son is eternally begotten of the Father;[63] the Holy Ghost eternally proceeding from the Father and the Son.[64]
It is not a contradiction to say that there is one God who exists in three persons. It would be a contradiction to say there be three persons, and to say there be not three person. Or to say God is made of one substance, and then to say he is made of three substances. This trinitarian God is mysterious indeed, but not a contradiction. The law of non-contradiction itself flows from the God who never contradicts himself. I could not say the same is true of me.
May our great three in one God bless you this Saturday!
Leading Family Devotions 