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 Hi TimBarrel (I do like your screen name) 
 The difference between “…reactions are extremely slow when not catalysed by enzymes” and  “…reactions would occur too slowly… without enzymes.” Is that the former is a statement of fact that can be tested, and needs no further explanation.  But what does it mean to say that reactions would occur too slowly without enzymes?  Too slowly for what?  How slow is too slow?  How fast must reactions go in order to support life?  One might say that uncatalyzed reactions go too slowly to support life.  But the slowness of change  in the absence of enzymes is actually crucial to life.  How slow do uncatalyzed reactions go?  A good answer would be “slow enough to support life”.  Because the great stability of organic molecules, their resistance to change in the absence of enzymes is just as important as the high rate of cellular reactions that are enzyme catalyzed. 
 :<> 

 I suggested that the original writer may have meant that in the absence of enzymes, different reactions would lead to different products and that the presence of enzymes would prevent this .  But my point was that enzymes would not prevent it.   A molecule enters different chemical reactions that do lead to different products.  This is what would occur in a test tube in the absence of enzymes, as molecules enter into a vast number of possible reactions going so slowly you could hardly detect them.  But in a cell, there are enzymes.  An enzyme will choose one reaction among all this vast number of reactions (going so slow you can hardly detect them) and cause it to go extremely fast. 

 All the textbook aren’t wrong, just most of them.  One of the worst examples was in a textbook we used for years, Biology.  7th ed.  Solomon, E. P., et. al.  Brooks/Cole-Thomson. 2005. Page 128 (this is a very widely used college textbook): “Cells cannot wait for centuries for glucose to break down, nor can they use extreme conditions to cleave glucose molecules.  Cells regulate the rates of chemical rections with enzymes, which are biological catalysts that increase the speed of a chemical reaction without being consumed by the reaction.” (Cells can’t wait for centuries!  It completely misses the point). 

 Contrast this with Biology.  Raven, P.H. et al.  McGraw Hill.  2005.  Page 149 (this too is a very widely used college texbook):  By facilitating particular chemical reactions, the enzymes in a cell determine the course of metabolism – the collection of all chemical reactions – in that cell.  (Very good. No drivel about fast enough to support life.  My problem is the text should take an additional page or two to explain further this profound idea.  In my view, enzymes are the clearest link between DNA and life). 

 The best I ever saw was in an old text on biological thermodynamics: The Vital Force: A Study of Bioenergetics.  Harold, F. M.  W. H. Freeman & Co. 1986.  Page 31. From the thermodynamic point of view, the conversion of nutrients into cell constituents can be regarded as a grand chemical reaction that proceeds with an overall decrease of free energy.  This is the warp of the metabolic web.  Its woof is the work of a multitude of enzymes that select the particular strands out of many that are thermodynamically possible in order to carry the flux of matter through the web. 

 And take a look at TimVickers comment immediately above.  It hits the nail on the head. "