In the context of John 4:23, it probably does mean worshiping in the power of the Holy Spirit. It would take a long time to explain fully what that means, but Jesus is looking forward to the fulfillment of His work. He is speaking to the woman at the well in John 4. He says, “The time is coming when you will no longer worship on this mountain, nor will you worship on the mountain of God” (John 4:21). He’s saying that the internationalization of the people of God, which happens on the day of Pentecost, means that place becomes irrelevant in worshiping God. What then becomes exclusively relevant is worshiping in truth.
If you read through John’s gospel, eventually it becomes clear that worshiping in truth means worshiping through Christ and worshiping in Jesus’ name. If you fast-forward to John 14:6, where Jesus says, “I am the way, the truth, and the life,” it’s almost as though John is saying at that point: “You were wondering what He meant in chapter 4 by saying, ‘You worship in truth.’ This is ultimately what He means: He is the way of access to the Father. ‘No one can come to the Father except through Me.’”
What is it that enables us to come to the Father through Christ? As the gospel goes on, Jesus explains more and more, and we see that this takes place through the ministry of the Holy Spirit. Jesus referred to that when He was discussing the question of the entry into the kingdom of God with Nicodemus in John 3, when He said, “You need to be born of the Spirit if you’re going to enter the kingdom of God.” He discussed that with the woman at the well when He said, “If you knew who I was, you would have asked me for a drink, and I would have given you living water” (John 4:10). As you read on in John’s gospel, it becomes clear that living water is a reference to the gift of the Holy Spirit.
Jesus may have said more to the woman at the well, but the way John is telling the whole story (and this is typical of him) is that he’s dropping hints that intrigue you and make you ask exactly that question: What does it really mean to worship in spirit and truth? As you keep reading John’s gospel, it becomes clear that it means to worship the Father through the Son, in the power of the Holy Spirit.