Then would you explain Gal 2:16 which says "faith of Christ"?
		
		
	 
The Greek "dia pistewv Ihsou Xristou" 
Dia:
through 
of place 
with 
in 
of time 
throughout 
during 
of means 
by 
by the means of 
through 
the ground or reason by which something is or is not done 
by reason of 
on account of 
because of for this reason 
therefore 
on this account 
So by means of Pistis:
conviction of the truth of anything, belief; in the NT of a conviction or belief respecting man's relationship to God and divine things, generally with the included idea of trust and holy fervour born of faith and joined with it 
relating to God 
the conviction that God exists and is the creator and ruler of all things, the provider and bestower of eternal salvation through Christ 
relating to Christ 
a strong and welcome conviction or belief that Jesus is the Messiah, through whom we obtain eternal salvation in the kingdom of God 
the religious beliefs of Christians 
belief with the predominate idea of trust (or confidence) whether in God or in Christ, springing from faith in the same 
fidelity, faithfulness 
the character of one who can be relied on 
We now have by means of belief (Faith) or conviction in of Iesous Jesus or Joshua as the Hebrew would be, Christos Christ,
Gal. 2:16 "Faith of Christ" is redendered from the Greek, through conviction or belief that Jesus Christ is the Messiah through whom we obtain eternal life.  The Textus Receptus bears it out, that is what the KJV is translated from.