INTRODUCTION.--An ancient writer informs us that when the Egyptians named their Greatest God who was over all, they cried thrice, "Darkness! Darkness! Darkness!" And when we come to speak of the great mystery of the Holy Trinity, the utmost we can do is to repeat their cry, and say, "Darkness! Darkness! Darkness! In the name of the Father--Darkness, and of the Son--Darkness; and of the Holy Ghost--Darkness!" for however much the mind may strive to penetrate this mystery, it can never attain to its solution. Just as the eye, looking at the sun, sees the Overpowering light as a dark ball, being dazzled by its excessive glory, so the eye of the mind perceives only darkness, when looking into the infinite splendour of God in Three Persons. We may, indeed, see sundry likenesses here on earth, which assist us in believing the doctrine of the Holy Trinity, but they are helps, and helps only; and not explanations. Thus, the sun may shine into a glass, and the glass reflect in clear water, and we see three suns, a sun in the heaven, a sun in the glass, and a sun in the water, which proceeds from both;--and this assists us to understand how the Son of God is of the Father, and the Holy Ghost is of the Father, and of the Son, and how that each is God, and yet that there are not three Gods, but one God. But, after all, the doctrine of the Holy Trinity is a matter of Faith, and not of Reason. We must believe, though we cannot understand. SUBJECT.--In this Holy Trinity of Persons there is perfect unity existing, an unity of substance, an unity of Godhead, an unity of perfection, an unity of love. And on earth, among men, there should be unity. "Be ye perfect," said our Lord, "even as your Father which is in Heaven is perfect." The Father is love, the Son is love, and the Holy Ghost is the love of the Father and of the Son, and this love requires the same of us--even love, or unity. This is what God wills on earth, our living unity, even as it exists in Heaven between the Three Persons of the glorious Trinity. But there are three great hindrances to Christian Unity.