In John 6, Jesus feeds 5000 men and their families with five barley loaves and two fish. The next day, Jesus says these words to the crowd he fed. "Do not work for the food that perishes, but for the food that endures to eternal life, which the Son of Man will give to you" (Jn. 6:27).
This teaching precedes the famous saying, "I am the bread of life; whoever comes to me shall not hunger, and whoever believes in me shall never thirst" (v. 35). Jesus has fed their bodies, and now, He promises to feed their souls.
Of course, they know He fed their bodies. Their full stomachs and the twelve baskets of leftovers testify to that. But how can they be certain He gives the food that endures to eternal life? How can they know He satisfies spiritual hunger and thirst?
We get the answer to those questions in these words: "For on him God the Father has set his seal" (Jn. 6:27). The seal testifies to Jesus' authenticity. The seal proclaims that Jesus' ministry belongs to and takes its cue from God the Father. The seal identifies Jesus as God's only begotten Son.
When did the Father set His seal on the Son? Most likely, it happened when John baptized Jesus. The Spirit descends as a dove and remains on Jesus. Then, John testifies to these words from the Father, "He on whom you see the Spirit descend and remain, this is he who baptizes with the Holy Spirit" (Jn.1:33).
The Father set the seal of the Spirit on the Son, and the Spirit's seal was made manifest in the powerful way in which Jesus cast out demons, healed the sick, and controlled nature. We hear Peter preaching this very truth in Acts 10. "God anointed Jesus of Nazareth with the Holy Spirit and with power. He went about doing good and healing all who were oppressed by the devil, for God was with him" (Acts 10:8).
So, the Father testifies to the genuine character and work of Jesus by the seal of the Spirit. The proof of that seal came out in the works Jesus did. And the ultimate vindication of Jesus as the Son of God came when, by the Spirit, He was raised from the dead (Rom. 1:4).
Now, as men and women hear the gospel and believe in Jesus, they are sealed with the same Holy Spirit (Eph. 1:13-14). The Spirit who testified to Jesus' authenticity as the Son of God now testifies to our authenticity as those adopted by God as sons (Eph. 1:5; Gal. 4:4-6).
The Spirit whose presence was made manifest in the works of Jesus is now made manifest through the fruit seen in our lives (Gal. 5:22-23). And the Spirit who raised Jesus from the dead will one day raise up these mortal bodies to be glorified forever (Rom. 8:11).
To think more about the seal of the Spirit in the Christian's life, listen to yesterday's sermon on Ephesians 1:13-14 (Soundcloud; iTunes).