William Symington, Historical Sketch of the Westminster Assembly of Divines (2002 PAP ed.), pp. 41-44:
Permit me, ere I conclude, to give expression to another fondly cherished hope. It must not be overlooked that the divines at Westminster contemplated, besides a religious uniformity in the three kingdoms, a grand Protestant Union throughout all the nations of Christendom. Their hearts were large, and the measures they conceived were catholic, generous, free. No sectarian prejudices, no weak partialities of kindred or of country were permitted to freeze or to confine the current of holy feeling that flowed in their bosoms. Their sympathies were universal as man; and their conceptions partook of the same lofty and munificent character. Their eyes penetrated beyond the limits of their own "sea-girt isle," and ranged freely over the nations of them that dwell on the face of the whole earth. Their hearts, receiving inspiration at the cross, throbbed full with not merely "glory to God in the highest," but "peace and goodwill toward men." They, consequently, opened correspondence with foreign churches, and, in the largeness and the warmth of their affections, formed schemes of co-operation and intercourse which, in Providence, they were not permitted to see realised. They wrote letters to the Churches of Zealand and Holland; and on one occasion Baillie speaks of a deputation appearing at the Assembly and delivering in a letter from the classis of Walcheren.*
The Westminster Standards, accordingly, breathe no contracted spirit - wear no local aspect. They are, on the contrary, catholic and generous in their bearing, and adapted equally to the church in Britain, on the continent of Europe, in the republican states of America, in India, the Islands of the Southern Pacific, and New Zealand. Well did the divines at Westminster know that the Christian Commonwealth acknowledges no national distinctions, and spurns all geographical restrictions; and they had before their minds, when framing their formularies, no such anomalous contradiction as a Roman-Catholic, or an Anglo-Catholic church, but simply, a catholic church.
It is pleasing to think that the magnificent idea of a Protestant Union appears to have originated with one of the commissioners from Scotland, - Alexander Henderson, - of whose greatness of soul it was every way worthy. In prosecution of the favourite conception, he had proceeded so far as to obtain a passport to Holland, which, however, like many other good projects at that period, was rendered useless by the intervention of political intrigue. It is to the same glorious enterprise that Baillie adverts when he thus beautifully and piously expresses himself:- "We are thinking of a new work over sea, if this church were settled. The times of Antichrist's fall are approaching. The very outward Providence of God seems to be disposing France, Spain, Italy, and Germany, for the receiving of the gospel. When the curtains of the Lord's Tabernacle are thus far, and much farther enlarged, by the means which yet appear not, how shall our mouth be filled with laughter, our tongue with praise, and our hearts with rejoicing."**
Such were the bright conceptions and noble aspirations of men whom it has been too much the fashion to stigmatise as narrow-minded bigots, - aspirations and conceptions which we do not the less regard with admiration that they were clearly in advance of the age in which they were formed. The far-reaching perspicacity and large philanthropy of the men fairly anticipated what ages should elapse before being realised. Are we to entertain the gloomy idea that these bright and glowing thoughts are all to be lost? Admitting they were premature, may they not yet be accomplished? Who can tell but that the period of their realisation is at hand? Who can tell but that the seed sown two hundred years ago, still instinct with life, is destined now to reach maturity, and to yield an ample and glorious harvest? Minds of kindred mould and energy have at length arisen; times remarkably coincident have arrived; some of the causes which hindered the hopes of these illustrious patriots from being fulfilled have had time to develop and to exhaust themselves; and we see not a few ready to join in the prayer of faith, "Turn thou us unto thee, O Lord, and we shall be turned; renew our days as of old." Therefore it is that we feel disposed to regard it as something more than a baseless vision of imagination which leads us to hope that the period is not distant when the mighty principles of the Westminster standards shall be more extensively recognised than they have ever yet been, and shall put forth an energy of influence on society hitherto unknown.
Let us mark, then, the indications, let us follow the leadings of Providence; let us prove ourselves, like the sons of Issachar of old, men of understanding to know the times and what Israel ought to do. Rising above the little jealousies of sectarian rivalry, laying aside all personal asperities, let us show a readiness to meet, on the arena of frank and friendly consultation, brethren of other denominations, and to discuss with them our points of difference in a spirit of Christian candour and charity. Surely the friends of the Redeemer are not to be for ever separated. The reign of disunion is not to be perpetual. "There is one Lord, one faith, one baptism; one God and Father of all, who is above all, and through all, and in all. There is one body and one Spirit." And, believing as we do that these statements of Holy Writ are to receive a visible as well as an invisible fulfilment, we must hold professing Christians bound to use all proper means for bringing this about.
Is it not more to be desired that the Churches of the Reformation, holding by the Westminster standards, should, like rational and moral creatures, come to unite on the basis of truth, by the blessing of God, on the scriptural use of mutual consultation, explanation, advice, and prayer; than that, like insensate masses, they should wait to be melted by the fire, and welded together by the hammer, of Divine judgments? That these meetings commemorate the men and the doings of former days may result in a closer union of Christians, must be the fervent desire of every enlightened friend of the Redeemer. No one who wishes well to the glory of Christ or the good of Zion, can derive satisfaction from the thinking that the dissensions and divisions of modern times are to be much longer perpetuated. Let us, then, crucify and repress the spirit of party strife; let us feed the flame of that sacred affection which many waters cannot quench, neither can the floods drown; let us stand prepared to take to our hearts, in fraternal embrace, all who love the Lord Jesus in sincerity; let us converse closely and oft with those predictions which foretell a coming period of unity and peace; and let us drink daily and deeply into the spirit of the intercession, "That they all may be one, as thou, Father, art in me and I in thee, that they also may be one in us."
May the Lord the Spirit give the ministers and members of the divided Churches of the Reformation one heart and one way, that they may fear him for ever, for the good of them and their children after them! Then - and not till then - should be fulfilled the great, the bright, the glorious conceptions of the Solemn League and of the Westminster Assembly; it being the explicit design of the latter "to bring the church at home into nearer agreement with other Reformed Churches abroad," and of the former, "to bring the churches of God in the three kingdoms to the nearest conjunction and uniformity, and to encourage other Christian Churches to join in the same or like association and covenant, to the enlargement of the kingdom of Jesus Christ; and the peace and tranquillity of Christ's kingdoms and commonwealths." When "the people" - the saints of the Most High - are "gathered together," then - but not till then -- shall "the kingdoms serve the Lord."
* Baillie, vol. 2, pp. 115, 117, 142
** Baillie, vol. 2, p. 192.