(a) superfluous and unnecessary; needless repetition of an act or speech.This first notion is certainly commonly accepted and clear. The question is, does it really reflect the true purpose and function of redundancy in the practical world?
Consider now these alternate modern definitions:
(b) repetition of messages to reduce errors in transmission;
duplication of components/functions to overcome component failure.
Plainly, the description in (b) suggests deliberate actions and choices that are anything but superfluous, needless, or unnecessary. And it gets right to the heart of the matter of the modern scientific perspective on "redundancy". Redundancy is simply not 'redundant' at all in the common meaning of the term. Its absolutely essential for the reliable function of both communications and mechanical machines that lives depend on.
Redundancy in human communications
Its easy to see that most human communication is heavily redundant. In the sense of efficiency in packing the maximum amount of information in the smallest package, human speech is by nature clumsy, inefficient, time-consuming, and often ambiguous and error-prone.
Information Theorists themselves express this inefficiency as follows:
"Redundancy in information theory is the number of bits used to transmit a message minus the number of bits of actual information in the message. Informally, it is the amount of wasted "space" used to transmit certain data. ..." (wikipedia)The idea here is that the same message could have been transmitted with less words. Notice the old definition creeping back in, even here. "wasted space"(!). Its as if the theorists have forgotten what the engineers have been insisting in all along. Redundancy isn't 'waste' - its critically important for reliability. We wouldn't want to eliminate redundancy in communication any more than we'd want to remove a safety railing beside Niagara Falls. Redundancy is built into every engineering structure, in the form of extra supports, extra-strong steel, materials and designs made to withstand disasters and part failures.
But is human communication really redundant in the first sense (a) = needless? We can all laugh at the stupidity of the guards in the famous Monty Python skit from the Holy Grail movie:
But the skit illustrates perfectly the problem of the ambiguity of human speech, and the need for repetition and explanation to assure that meaning is communicated clearly and effectively.
The Bible is a message placed in the form of human communication, and not surprisingly, there are ample instances of redundancy in it. In the Old Testament, we may note the parallel accounts of the books of Kings and the books of Chronicles, or the passages in the middle of Isaiah, duplicating the same stories as those found in Kings (Isaiah ch. 36-39 etc). In the NT, we have three gospels with largely duplicated materials, and many of Paul's letters dealing with the same topics in different words. Even at the verse-level, Hebrew poetry and prose often repeats an idea or sentence in alternate words.
Redundancy serves several functions in the Bible.
(a) it can fill in detail, and bring precision to a picture.
(b) It can provide alternative expressions to protect the meaning, for those with limited vocabularies.
(c) It can protect message of the Holy Scriptures from damage through wear, copying, and even tampering.
Redundancy in the Bible plainly fulfills important purposes, and cannot be viewed as 'redundant' in the common sense, as if repetitions were needless, or alternate expressions were merely 'wordy'. The Holy Scriptures have been designed in part by their own authors to reach the widest audience, and maintain the purity of the message by thoughtful use of repetition and alternate expression.
Biblical redundancy is one of the deliberate means used by Bible authors to protect the message of the Holy Scriptures for future generations. In the days of handcopying, parallel passages in Mark, Luke and Matthew could be compared for accuracy in transcription of the message. Passages in Paul could be compared to ensure Paul's meaning was well understood. Redundancy is in that sense what Bible study is all about.