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In this form it is clear that we can perform separate global flavour transfor- mations on ψ$_{L}$ and ψ$_{R}$ . Since the quarks are in an SU(2) isospin multiplet, we write these transformations as SU (2)$_{L}$ ⊗ U (1)$_{L}$ and SU (2)$_{R}$ ⊗ U (1)$_{R}$ respectively. The Lagrangian is unchanged by these transformations: it is chirally invariant. (The analysis still holds if we turn on the gauge field A$_{µ}$ .) 

However, this is a symmetry of the Lagrangian which is broken sponta- neously by the choice of vacuum. The most obvious manifestation of this is the absence of a parity-doubled spectrum. If the chiral symmetry was respected, there would be a positive parity hadron for every negative parity hadron. This is not what is seen in nature. For example, the proton has isospin 1 $_{2}$, spin 1 2 and a positive parity. Its mass is 938 MeV. Its parity part- ner, catchingly called the N(1535) S$_{11}$ , has a mass of 1535 MeV [24]. We conclude that chiral symmetry is broken at a quantum level, and the easi- est way to account for this is by assuming that QCD spontaneously forms a quark condensate. In other words, the QCD vacuum gives a non-zero vacuum expectation value to the scalar operator 

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What is the physical interpretation of this VEV? The up and down quarks are very light, and so it costs little energy to create a quark-antiquark pair. However, the binding energy released by a bound quark-antiquark pair is large. All (1.33) is saying is that the process of forming a quark-antiquark pair and then binding them together is exothermic: we get out more energy then we put in. 

The vacuum expectation value (1.33) means that we can no longer perform independent gauge transformations on the left and right handed 

