Clue: Slightly backtracking, show deference to biblical couple going steady (2,2,4,4)
Answer: ON AN EVEN KEEL
Explanation: Definition: going stead
A charade of ONAN plus EVE ('biblical couple' – in as far as they both feature in the Old Testament) plus NKEEL, which is KNEEL ('show deference') with the first two letters reversed ('slightly backtracking').