Philippians 1:10 Word Study

Vs 10 "so that you may approve the things that are excellent, in order to be sincere and blameless until the day of Christ."
Sincere = eilikrines - to shine, the sun (eili) + to judge (krines)  It also can mean pure.  Guileless, transparent, or  acting with full disclosure.  The word originates with the Greek market for pottery.  There were two kinds of potter: real (or sincere) and fake.  The fake potters would take bits of old pots and form a new pot using a form of wax.  The customer could judge whether it was real pottery by holding it up to the sun.  The sun would shine through the wax though, allowing the customers to know if it was real or fake. Hence the genuine pottery was called 'sincere'. 
Blameless (forgot to write down the Greek word) - to not offend or cause others to stumble.  This is not generally used to mean without sin. It is the word used in various letters by Paul when he says to be pleasing to others (See 1Cor. 10:31-11:1) so as not to offend them, in order that they might be saved.

So we are to be sincere (not hypocritical or deceptive) and blameless (being the kind of person that others want to be around, even when we differ in our beliefs) in our faith.

- Erika