This book by William Carruthers is a facsimile of the Westminster Shorter Catechism, but there is a rather extensive bibliography at the end which lists, among other things, expositions of the catechism.

The Shorter Catechism of the ... - Google Book Search

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Brian Kooshian
Member, Reformed Baptist Church of Holland
Zeeland, MI
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"I once was an Armenian Arminian. Now I'm an Armenian Calvinist!"