John 1:14

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.

John has been describing, supporting, and demonstrating what he summarizes and crystallizes in this verse—God became a human being. The creator entered into and willfully became part of His own creation. From the very beginning, God desired to dwell among His people. Under the Old Covenant and through the rituals of the Old Testament sacrificial system, God dwelt among His people but He had to veil Himself because of their unrighteousness. In this action of becoming part of His own creation, He will forever remove the veil between Him and His people by imputing His own righteousness onto His people through the sacrificial death and resurrection of His son Jesus Christ.

The Greek word (doxa) translated to glory, literally means opinion.
The glory that Jesus shone—that John describes here—is literally the Father’s opinion of Jesus (Matthew 3:17 “…and behold, a voice from heaven said, "This is my beloved Son, with whom I am well pleased.") Jesus was absolutely perfect in every respect; in a way no other human being could ever be.

His grace and His truth is what we were able to see in the person of Jesus Christ.
In Genesis when the Lord gave Moses and (by extension) Israel the second set of tablets containing the Ten Commandments, He did so out of covenant-keeping gracious love. It is this abundant love and grace that is now revealed in Jesus. Jesus goes on to do what the Law, and the Old Covenant sacrificial system, could never do; provide for His people a way of salvation from their own sin.

John links grace and glory; emphasizing Jesus’ deity (ultimate and sovereign power and authority) and His grace upon His creation. God Himself was the only being qualified to atone for the sin of mankind (i.e., glory), and He chose to do it because of His great love for us (i.e., grace).