This passage shows what people are and what they can do without the protection of the Spirit. They are orphans, exposed to every kind of fraud and injustice, incapable of governing themselves, and in short unable of themselves to do anything. The only remedy for such a great weakness is for Christ to rule us by his Spirit, which he promises to do. First, then, the disciples are reminded of their weakness, so that they distrust themselves and rely only on Christ’s protection. Second, having promised a remedy, he raises their hopes, for he says that he will never leave them. When he says, “I will come to you,” he is showing how he will live in his people and how he fills everything. This is by the power of his Spirit, and so it is clear that the grace of the Spirit is striking proof of his divinity.
Calvin, J. (1994). John (Jn 14:18). Wheaton, IL: Crossway Books.