How do we know grace and truth came by Jesus Christ?

The distinction between the law given by Moses and the grace and truth coming through Jesus Christ is critical in understanding the gospel. John 1:17 clearly states that the law was given through Moses, but grace and truth came by Jesus Christ. This signifies that while Moses' law highlighted human guilt, it was Christ who came to fulfill the law perfectly and to establish righteousness through His life, death, and resurrection. In Christ, righteousness is fulfilled for His people, marking the transition from the old covenant of law to the new covenant of grace, where His fullness offers grace for grace.