How does the Spirit empower our unity? As we have seen, the Father now speaks to us by His Son (Hebrews 1:1). Jesus is the one Shepherd whose voice gathers one flock (John 10:16, 27). But how are they to hear Him today, so long after Jesus ascended to the Father? That is the work of the Holy Spirit.
In the Old Testament, the Holy Spirit inspired the prophets to deliver God’s messages.
You gave Your good Spirit to instruct [the Israelites]. … Many years You bore with them and warned them by Your Spirit through Your prophets (Nehemiah 9:20, 30 cf. 2 Samuel 23:2; Mark 12:36; 2 Peter 1:21).
While Jesus lived on earth, He worked “in the power of the Spirit” (Luke 4:14 cf. Matthew 12:28). The Son spoke for the Father because He received “the Spirit without measure,” that is, without any limit (John 3:34).
[Jesus said,] “The Spirit of the Lord is upon Me, because He has anointed Me to proclaim good news …” (Luke 4:18 cf. Matthew 12:18).
[Jesus] was taken up [to heaven], after He had given commands through the Holy Spirit to the apostles whom He had chosen (Acts 1:2).
While still with the apostles, Jesus prepared them for His departure. He promises them that, from heaven, He would send the Holy Spirit to empower them for His message (Acts 1:8 cf. Acts 2:4, 33).
I will ask the Father, and He will give you another Helper, to be with you forever, even the Spirit of truth. … The Helper, the Holy Spirit, whom the Father will send in My name, He will teach you all things and bring to your remembrance all that I have said to you (John 14:16, 26).
But when the Helper comes, whom I will send to you from the Father, the Spirit of truth, who proceeds from the Father, He will bear witness about Me (John 15:26).
It is to your advantage that I go away, for if I do not go away, the Helper will not come to you. But if I go, I will send Him to you. … I still have many things to say to you, but you cannot bear them now. When the Spirit of truth comes, He will guide you into all the truth, for He will not speak on His own authority, but whatever He hears He will speak, and He will declare to you the things that are to come. He will glorify Me, for He will take what is Mine and declare it to you (John 16:7, 12-14).
The Spirit guided the apostles into all the truth.
The one Spirit would ensure that the one Lord’s teachings would remain accurate and complete as they were entrusted to His spokesmen, the apostles. They would remember what Jesus had taught them (John 14:26), and they would receive all that remained to be taught (John 16:12-13). Thus, “all the truth”—certainly all the truth we need to know—was delivered (2 Peter 1:3; Jude 1:3). It was recorded in the New Testament Scriptures so that now we, the sheep, can hear the voice of the one Shepherd.