The verse is saying the Lord credited it to him. In a way salvation is the same under all convenants. Before the cross salvation came by believing and obeying what God said. The real redemption is the 1st ressurrection.
Ephesians 1
13 In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise,
14 Which is the earnest of our inheritance until the redemption of the purchased possession, unto the praise of his glory.