The "St. Andrew's cross," in form like the letter X, conveys the idea of humility as well as that of suffering. When St. Andrew was condemned to be crucified, he begged that his cross might be unlike that on which his Lord had died, not deeming himself worthy to die on a cross of the same form as that on which He had suffered.
St. Andrew's cross
There is a cross peculiar in form, and known as the "Canterbury cross." It is in the shape of the letter Y, and is usually seen only upon the vestments of the clergy. The ornamentation of the chasuble is commonly of this form. It is embroidered on the chasuble of St. Thomas of Canterbury, which is still preserved in the Cathedral of Sens, in France. Its shape brings to mind the inclination of our Saviour's arms—the lifting up of His hands—as He offered Himself in sacrifice on Calvary.
Symbols of the Holy Trinity.—The equilateral Triangle is perhaps the most familiar emblem of the Holy Trinity. The equality of the three divine Persons in the Godhead is represented by the equal sides or the equal angles of the triangle.
Triangle
The Trefoil is also an emblem of the Trinity. It is a representation of the common clover, or shamrock, as the Irish call it. The legend of the conversion of Ireland says that St. Patrick was preaching on the hillside, and wishing to illustrate from nature the sublime doctrine of the Trinity to his pagan hearers, he bent down and plucked a piece of shamrock at his feet, and held it up to show how what was three, in one sense, might be one in another.