I’m probably going to talk about common themes later, but I noticed something interesting that might not be the first thing one would notice in these passages, and that’s a combined sense of inadequacy without God’s Spirit, and the adequacy given by the presence of God’s Spirit. In Isaiah 49, the servant is taken as an infant, and equipped by God. This parallels John 1, I think, where we do not have an expression of inadequacy, but we have the giving of the Spirit at baptism, and ministry that follows it.
Inadequacy is specifically expressed in Psalm 40:1-11 “pulled me up from the seething chasm” and “from the mud of the mire” (v. 2, NJB), and in Paul’s letters frequently, but demonstrated in our passage again through the focus on “called by the will of God (v. 1), and “relying on God” (v. 9).
Whether or not the inadequacy is expressed, in each case the preparation and the giving of the Spirit is the launching point for ministry. We talk about the baptism of Jesus as demonstrating the path that each Christian must follow. Jesus is obedient to God, even though he has not sinned and doesn’t require baptism for forgiveness of sins. But note also that Jesus is not inadequate, as we would normally think of inadequacy, but he also launches his ministry when he receives the Spirit.
There is a pattern there for modern ministry (clergy or lay) as well.