Why have we been discussing respiration at all – neither O2 has come into the picture nor the promised large number of ATP has yet been synthesised till Kreb's cycle. Also what is the role of the NADH + H+ and FADH2 that is synthesised in Kreb's cycle?

Why have we been discussing respiration at all – neither O2 has come

1.	Why have we been discussing respiration at all – neither O2 has come into the picture nor the promised large number of ATP has yet been synthesised till Kreb's cycle. Also what is the role of the NADH + H+ and FADH2 that is synthesised in Kreb's cycle?
Answer» Why have we been discussing respiration at all – neither $O_{2}$ has come into the picture nor the promised large number of ATP has yet been synthesised till Kreb's cycle. Also what is the role of the $N A D H$ + $H^{+}$ and $F A D H_{2}$ that is synthesised in Kreb's cycle?