Instead of goal, other translations speak of being perfected.
The idea is that human effort/works of the flesh are needed in order to make progress in the Christian life.1 In the context of the Galatians, they thought that circumcision and obedience to old covenant law would bring them closer to God, as if the Spirit is not sufficient. Paul responds with a question that is meant to help them understand that the Christian life is supernatural (Spirit-led) from start to finish.2
3 Are you so foolish? Having begun by the Spirit, are you now being perfected by the flesh?