20 At that day you will know that I am in My Father, and you in Me, and I in you.
The apostles, after Jesus’ resurrection, would acknowledge the relationship of the Father and Son as well as the relationship between Christ and His followers.
Union is the pattern for relationships. The Holy Spirit would indwell each believer permanently during the new economy or dispensation of the church—albeit the relationship between Christ and the believer is not the same as between Christ and the Father.
20 At that day
The words “that day” often refer to an epoch, a period that is unique in God’s economy. The words “that day” refer to the resurrection of Jesus from the dead and the day of Pentecost, the descent of the Spirit, the day the Holy Spirit would come to permanently indwell the church.
you will know that I am in My Father,
As a result of the resurrection and coming of the Holy Spirit to permanently indwell the church, the apostles would know that Jesus was in the Father and believers were in Him (Jn 12:16; 16:12-15).
and you in Me,
Believers would be “in” Jesus. They would experience union with Christ.
and I in you.
There is a mutual indwelling between Jesus and His followers. On the day of Pentecost, Jesus would live in believers. This transformation of the apostles went far beyond His resurrection. Their relation to Him would rise to a newer plane. Jesus would be a constant presence with the apostles.
There would be a categorical change in the relationship with Christ after the resurrection.
The relationship between the Father and Son is one of essence. The union is absolute, incapable of change. The relationship between Christ and the believer is positional and spiritual. The believer’s eternal status or union with Christ will never change; it is an eternal relationship. We will see in the next chapter that Jesus is the vine; we are the vine branches.
In a few weeks after the resurrection, the apostles’ categorical perceptions changed:
They clearly saw that the Son is “in the Father”; that is, they recognized the deity of Christ. He is co-equal and co-eternal within the Trinity.
They knew that “you in Me” meant that they were in union with Christ. This began historically on the day of Pentecost.
They understood what “I in you” meant: Christ dwelling in the believer for the purpose of fellowship and the Holy Spirit indwelling the believer for operational purposes.