a Christ slave
The acumen "aCs" is an abbreviation for "a Christ slave".
One of the key attributes of a Christian is fully understanding their relationship to our Lord and Saviour Jesus Christ. Although Jesus elevates us to call us friend, brother or sister we must find joy and understanding in truly knowing our place. Jesus is one divine aspect of the Trinity that has existed for eternity in our time dimension but he is also the very triune God that created the universe.
What a privilege and joy it is to be able to know this with absolute certainty but to walk in humility as a slave of Christ. Jesus paid (bought us) with his blood on the cross at Calvary.
There is a brilliant book John MacArthur "Slave" which lays out the true relationship that we should have with our triune God and explains in detail how we can truly become passionate followers of Jesus Christ.
I am often asked to define "aCs" as I use it along with "PfoJC" as a title. Because of the gross misuse of the word "Christian" and the total misunderstanding in the world at large I do prefer to use "aCs".