It would be a mistake . . . to see the accounts of Jesus’ conception as the biological explanation of the Incarnation. Luke asserts that the Holy Spirit “overshadowed” Mary (Luke 1:35; cf. Matt. 1:20); episkiazw, used here, is again used in his account of the Transfiguration (Luke 9:34). To Jewish minds, this almost certainly pointed back to the divine cloud which covered the Israelites’ camp in the desert. This cloud was the mysterious presence of God visually presented. Perhaps we also have a parallel here to the creation account. In both, the Spirit is active; in both, he imparts life. What emerges from the Spirit’s creative work in the beginning was called “good”; what emerges from this work in Mary is called “holy.”What this affirms, then, is that Jesus was born without the involvement of a human father and that his humanity was created through Mary. Such a conception did not itself guarantee Jesus’ divinity, although it was certainly compatible with it; what it affirmed was that Jesus’ humanity had a supernatural origin. The reason that Jesus was not sinful had less to do with the mode of his conception than it did with the uniqueness of his being. It was because he was divine that he did not sin, and his taking of flesh through Mary in this fashion was a taking of that kind of flesh in which he, as God, could be in union. There was, therefore, no reason to explore the circumstances of his conception in order to explain his sinlessness if, implicitly and explicitly, he had made it clear who he was.
David F. Wells, The Person of Christ: A Biblical and Historical Analysis of the Incarnation (1984; reprint, Alliance, Ohio: Bible Scholar Books, 1992), 42-43.