Why was the gift of the pure boy attributed to Gabriel (peace be upon him) in the Almighty's saying: "He said, 'I am only a messenger of your Lord to give you a pure boy,'" instead of to Allah, the Almighty?

The Giver to Mary is Allah Almighty. Gabriel’s saying, peace be upon him, “(to give you)” according to the reading of the majority, or “(that he may give you)” according to the reading of Abu Amr and Warsh, is to be understood as Gabriel, peace be upon him, being the cause of the gift through his blowing into the garment, or that Gabriel’s saying is a narration of Allah Almighty’s saying to him: “(I have sent you to give a boy),” or that he attributed the gift to himself to inform her of it. The most accurate view is that Gabriel was a cause of the gift through his blowing.