With the expression grace and truth,
John is most probably directing his readers to Exodus 33:1 – 34:35, where Moses pleaded with the Lord to show him his glory (Exodus 33:18). God then told him that his glory is supremely seen evident in his goodness (Exodus 33:19). He is thus making the point that the glory of God revealed to Moses was the very same glory that John and his friends saw in the Word made flesh.1
In addition however, we can also say that grace and truth refers to the way in which Jesus carried himself before a watching world. Since he came to make God known, it is not surprise that his conduct throughout his life was consistent with who God is.2 He lived in a way that was in keeping with his nature as the Father’s only begotten Son.3
14 And the Word became flesh and dwelt among us, and we have seen his glory, glory as of the only Son from the Father, full of grace and truth.