John says that the Word made flesh is 'full of grace and truth.' The phrase can sound like a general compliment about kindness and honesty, but its biblical resonance is considerably richer.
The wording closely recalls the Greek-scriptural expression of God's steadfast, faithful character revealed to Moses.
In Exodus 34:6 God proclaims his name and character to Moses as abundant in steadfast love and faithfulness. The Septuagint and John's Greek are not mechanically identical, but the pairing of grace and truth is widely understood against this covenantal background, especially because John immediately contrasts the giving of the law through Moses with grace and truth coming through Jesus Christ.
John's prologue also speaks of beholding Jesus' glory, another major Exodus theme.
The Exodus background means John is doing more than comparing two religious teachers. The divine character disclosed to Moses is now revealed personally in the incarnate Word.
That makes 'grace and truth' part of John's high Christology: Jesus does not merely explain God's faithfulness from a distance; in him God's glory and character are made known in flesh.