The significance of "Abba" in Romans 8

[Cow Poke]

vs 15 For ye have not received the spirit of bondage again to fear; but ye have received the Spirit of adoption, whereby we cry, Abba, Father.

I have found in a commentary (Vine's) on the Mishna that it was supposedly forbidden for slaves to refer to the head of the family as Abba. Does that hold up? What else do we know about "Abba".

Particularly, I'm interested in the use of "Abba" in Romans 8.

[Littlejoe]

I know that because of the high importance of family ties to that culture, that it was sinful and even illegal in some areas to claim any family connection when there wasn't one. IIRC, it may even have been against Roman Law.

[Bill the Cat]

vs 15 For ye have not received the spirit of bondage again to fear; but ye have received the Spirit of adoption, whereby we cry, Abba, Father.

I have found in a commentary (Vine's) on the Mishna that it was supposedly forbidden for slaves to refer to the head of the family as Abba. Does that hold up? What else do we know about "Abba".

Particularly, I'm interested in the use of "Abba" in Romans 8.

Take a look here, CP:

http://www.ancientbiblehistory.com/facts/abba.html

In the case of a master with no heir, a favorite slave might be adopted for the sole purpose of having a legal heir to inherit the master's estate. In ancient times, a slave was never permitted to use the term Abba (father) or Imma (mother) when approaching the master or mistress for conversation. But after the adoption, the slave was considered a full son and was entitled to call the master father and the mistress mother.