The two things that Jesus emphasizes here are – The whole of mankind’s sinfulness is presupposed, but that even as fallen human parents, we still know instinctively & by natural love how to give good gifts not harmful ones to our children. The other is, as Christians we have been given the wonderful gift of the Holy Spirit ( Who teaches, enlightens, and guides us in respect to faith & practice) in response to our faith-filled prayers by a loving & good Heavenly Father. So for those who call on Father God…have come to know Him and are reconciled to Him through His Son, Jesus Christ…we can confidently trust that our good God will only give good gifts.