I realize this question is very broad but may be I will still get a helpful answers. References and textbooks for the development of the technical and mathematical aspects of QFT abound. However, I never came across a source dealing with the conceptual issues of QFT. I am interested in stuff like,
the meaning of Gauge symmetry,
Spontaneous symmetry breaking,
interpretation of renormalization group,
Are there any reference that deals with these issues mainly?