Barley is difficult to process into wort. It does not mill easily, it lacks appropriate levels of enzymes for starch and protein conversion, and the starch is not easily accessible. And it lacks malty flavour. Germination corrects for most of these deficiencies, and kilning takes care of flavour. Some beers are produced from barley alone, using exogenous enzymes. The attraction of such beers lies in their favourable tax treatment, not usually in their quality or ease of production. 

Historically, kilning was introduced both as a preservation method, and as a means of introducing flavours. Pale malts are a modern invention - historically, most malts have been dark. Significantly, kilning takes place in a stream of air, rather than in inert gas, allowing ample opportunity for reaction of malt components with oxygen. Such reactions can be both enzymic and non-enzymic. They can be beneficial (eg oxidation of flavoursome dimethyl sulphide to flavourless dimethyl sulphoxide), or deleterious (eg oxidation of malt unsaturated fatty acids via the action of lipoxygenase 1). 

Kilning reduces the levels of live microorganisms, minimizing their impact in the mashing process. But, enzymes associated with dead organisms may still be significant to beer quality.