言う, 云う, 謂う, いう, ゆう
1. to say, to utter, to declare
2. to name, to call
3. to go (e.g. "the alarm went ping"), to make a noise
のです, のだ, んです, んだ
Expression, の and ん add emphasis
the expectation is that ..., the reason is that ..., the fact is that ..., the explanation is that ..., it is that ...