Matthew 1:20

Fear not to take, &c. i.e., fear not to marry her, if we suppose them not yet married, or if married already, the sense is, fear not to keep and remain with thy chaste wife; lay aside all thoughts of dismissing and leaving her. (Witham) --- As the incarnation of the Son of God was effected by the whole blessed Trinity, it may be asked why this operation is peculiarly attributed to the Holy Ghost, not only here, but in Luke ii., and in the apostles' creed? The answer is, because as power is attributed to the Father, wisdom to the Son, so goodness is attributed to the Holy Ghost, and the gifts of grace which proceed from it. (Estius in different location)