The Protestant Reformers have oft been seen as divisive figures, responsible for the multiplicity of denominations and splintering of the church that's occurred over the last 500 years. A number of scholars, however, have been questioning that view, opting to see (at least the Magisterial) Reformers as concerned more with reforming and renewing the church, rather than forming a new one. Their goal was not a new church but a reformed Catholic church.
Looking at Calvin's Preface to his Genevan Catechism (1545), we see just this sort of ecumenical imperative. His vision of unity is thoroughly Pauline:
"Seeing it becomes us to endeavour by all means that unity of faith, which is so highly commended by Paul, shine forth among as, to this end chiefly ought the formal profession of faith which accompanies our common baptism to have reference. Hence it were to be wished, not only that a perpetual consent in the doctrine of piety should appear among all, but also that one Catechism were common to all the Churches."
His hope is that the church could achieve a unity of faith, or, as he puts it: "perpetual consent in the doctrine of piety." Ideally, this would mean there would be only one catechism among all Christians.
But this is, "for many causes," not likely going to happen, and that doesn't seem to bother Calvin too much. It's okay if each church has its own catechism, so long as "the variety in the mode of teaching is such that we are all directed to one Christ, in whose truth being united together, we may grow up into one body and one spirit, and with the same mouth also proclaim whatever belongs to the sum of faith."
This Christo-centric vision of a united church is often missed among Protestants, but it's well worth recovering if our aim is a thoroughly Reformational church.
He is particularly stern for those who in their catechism writing would intend anything but the building up of the unity of the church. A scandal against the confession of faith is a scandal against baptism—that is, without one faith, how can there be one baptism?
"Catechists not intent on this end, besides fatally injuring the Church, by sowing the materials of dissension in religion, also introduce an impious profanation of baptism. For where can any longer be the utility of baptism unless this remain as its foundation — that we all agree in one faith?"
You get the sense (or you at least hope) that Calvin has one finger pointed towards other writers and three pointing back at himself when he writes:
"Wherefore, those who publish Catechisms ought to be the more carefully on their guard, by producing anything rashly, they may not for the present only, but in regard to posterity also, do grievous harm to piety, and inflict a deadly wound on the Church."
Calvin is concerned that writing catechisms doesn't become a means of division, but a means of unity. And those who would write new catechisms must not only think of the current generation but future generations as well.
This imperative for unity also undergirds his decision to write a second edition of the catechism in Latin. He'd originally written in the vernacular French, but then decided to write in Latin. One of the reasons he does this (the other being so that people won't discontinue using his earlier catechism) is to advance the cause of a united confession of Christ, so that churches divided in space and time would be able to recognize one another in Christ. Latin is still the language of the western church at this point.
"In this confused and divided state of Christendom, I judge it useful that there should be public testimonies, whereby churches which, though widely separated by space, agree in the doctrine of Christ, may mutually recognize each other. For besides that this tends not a little to mutual confirmation, what is more to be desired than that mutual congratulations should pass between them, and that they should devoutly commend each other to the Lord?"
Calvin's take on catechismal unity may be somewhat naive—and of course he couldn't predict the future of Protestantism. But he is no doubt sincere in his efforts to build up the unity of the church. We cannot doubt that the Reformers aimed, not for sectarianism, but for one, holy, catholic, and apostolic church.
Especially given the fact that later catechisms sometimes degenerated into tools for affirming denominational particularism—as polemical weapons aimed at competing denominations—it is all the more important to recover this Reformational aim of ecumenical catechesis.
Catechesis, first and foremost, focuses on grounding believers in the basics of the faith, what the church has "always, everywhere, and at all times" held. This is why catechesis is closely linked to baptismal faith. One faith, one baptism—therefore one catechism. But if not, let us at least re-engender the unity of faith as the goal of catechesis.