Where is John 5:4?

Question: Why is John 5:4 not there except for the italics down the bottom?

Answer:
The answer to this question lies in how the New Testament is put together. There are many manuscripts that make up the New Testament as we know it. Lots of manuscripts agree with each other over the overall content of the New Testament which SHOUTS to its reliability as a document.

However there are some minor discrepencies between manuscripts and here in John 5:4 is one of them. Hence the note at the bottom of the NIV, b3.

Some less important manuscripts .... and then they add in v4 the piece of text from those other manuscripts.

In each case you have to weigh up with it should be included in the narrative or not by looking at whether it fits into the the book (internal evidence) and then whether it matches up with other manuscripts (external evidence) e.g. is it the only manuscript with this rendering. The NIV sometimes puts it at the bottom but most of the time it is totally unseen in the English translations.