I read Matthew 1:18-20 today. I realized again, how much rubbish it is every time I hear something to the effect of the Holy Spirit not having much of a role before Pentecost. It struck me that I usually only think of Jesus' relationship to the Holy Spirit in his sending him to the disciples after his ascension. Here, though, is another aspect. Without the Holy Spirit Jesus never would have shown up on this earth at all. The Holy Spirit was working to effect the incarnation.
I love to see different aspects of the Trinity. It's easy for me to forget about these things. God's Spirit was active in the incarnation, just as he was hovering over the waters at creation. Yet another reason to sing "Spirit, I adore you. I lay my life before you. How I love you."