Faith and Faithfulness (Part 8)

This is the eighth in a series of studies on the topic of faith and faithfulness. (If you are coming to this page from a search engine, I recommend this link for a table of contents of the topics covered in this series.)

In this study I would like to look at the word apistos (απιστος – G571), as it is used in the Septuagint, to see what it can tell us about pistis (πιστις – G4102). 

Thayer's Lexicon is available in the Internet Archives.    The page defining apistos can be seen here (on the lower left corner of page 57).  Here are images from that page.  The first definition is for apistia (απιστια – G570), a word that is not used in the Septuagint.

Notice that in the definitions for both words— apistia and apistos— that the first meanings are unfaithfulness and unfaithful. 

Apistos is used in two verses in the Septuagint; in Proverbs 17:6 and Isaiah 17:10.  Here are these verses as translated in the New English Translation of the Septuagint (NETS).  (The links are to the PDF files containing the NETS translation of the book.)  Neither of these two verses correspond exactly to the Hebrew text, so it isn't helpful to compare it with the Hebrew (or English translations from Hebrew).

Prov 17:6 – Children's children are a crown for the aged, and their fathers are the boast of children.  6a  The faithful (πιστου – pistou – G4103) has the whole world full of money, but the faithless (απιστου – apistou – G571) not even a farthing.

Isaiah 17:10 – Because you have abandoned God your savior and have not remembered the Lord your helper, therefore you will plant an unfaithful (απιστον – apiston – G571) plant and an unfaithful (απιστον – apiston – G571) seed.

Here are the same Septuagint texts in the Brenton translation. 

Prov 17:6 – Children's children are the crown of old men; and their fathers are the glory of children. The faithful has the whole world full of wealth; but the faithless not even a farthing.

Isaiah 17:10 – Because thou hast forsaken God thy Saviour, and hast not been mindful of the Lord thy helper; therefore shalt thou plant a false [margin: Gr. faithless] plant, and a false seed.

The reason I am looking at these translations from Greek isn't to say that they are better (or worse) than the translations from Hebrew; rather, it is to see examples of the word used in an Old Testament context so that we can use them as evidence in understanding the same word in a New Testament context.

Which meaning of apistos makes better sense in this context?  Is it a contrast between the loyal and disloyal, the honest and dishonest, the reliable and unreliable, the faithful and unfaithful?  Or is it a contrast between the believing and unbelieving?  In Isaiah 17:10, isn't abandoning and forsaking defining what it means to be unfaithful— to be apistos?