What is "effectual calling"

Effectual \Ef*fec"tu*al\ (?; 135), a. [See Effect, n.] Producing, or having adequate power or force to produce, an intended effect; adequate; efficient; operative; decisive.
--Shak.

Effectual steps for the suppression of the rebellion.
--Macaulay.

Effectual calling (Theol.), a doctrine concerning the work of the Holy Spirit in producing conviction of sin and acceptance of salvation by Christ, -- one of the five points of Calvinism. See Calvinism.

Syn: Effectual, Efficacious, Effective.

Usage: An efficacious remedy is had recourse to, and proves effective if it does decided good, effectual if it does all the good desired.
--C. J. Smith.

Effectual calling (or effective calling) 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." Grudem appeals to the story of Lydia: according to Acts 16:14, "The Lord opened her heart to respond to Paul’s message" ( NIV).