Effectual calling (or effective calling[1]), in Calvinist Christian soteriology, is a stage in the ordo salutis in which God calls a person to himself.
It is connected with, but different from external calling, in which a person hears the gospel message.
Wayne Grudem suggests that it is a summons from the King of the universe that has "such power that it brings about the response that it asks for in people's hearts.
"[1] Grudem appeals to the story of Lydia: according to Acts 16:14, "The Lord opened her heart to respond to Paul’s message" (NIV).
[2]