The Deposit of Faith, towards a definition

What is the apostolic deposit of faith?  This question is hard to answer in a non-circular manner.  The implied answer among all traditions is “Whatever we are already teaching now.”  Such a position is impossible to prove.  For all of the evils of liberal/critical biblical scholarship, they did shed important light on the manner.  If we focus on the apostolic kerygma, we see an emphasis on Christ’s death and resurrection according to the Scriptures.   So what is the apostolic deposit?  To quote an older liturgy, “Christ has died.  Christ has Risen.  Christ will come again.”