J. C. Ryle, Old Paths (London, 1898), 259:
The cross is the grand centre of union among true Christians. Our outward differences are many, without doubt. One man is an Episcopalian, another is a Presbyterian,—one is an Independent, another a Baptist,—one is a Calvinist, another an Arminian,—one is a Lutheran, another a Plymouth Brother,—one is a friend to Establishments, another a friend to the voluntary system,—one is a friend to liturgies, another a friend to extempore prayer. But, after all, what shall we hear about most of these differences, in heaven? Nothing, most probably: nothing at all.
Does a man really and sincerely glory in the cross of Christ? That is the grand question. If he does, he is my brother: we are travelling on the same road; we are journeying towards a home where Christ is all, and everything outward in religion will be forgotten. But if he does not glory in the cross of Christ, I cannot feel comfort about him. Union on outward points only is union only for a time: union about the cross is union for eternity. Error on outward points is only a skin-deep disease: error about the cross is disease at the heart. Union about outward points is a mere man-made union: union about the cross of Christ can only be produced by the Holy Ghost.
(HT: Tony Reinke)