God calls with respect to men when he designates them to some special office (Exodus 31:2; Isaiah 22:20; Acts 13:2), and when he invites them to accept his offered grace (Matthew 9:13; 11:28; 22:4).
In the message of the gospel, his call is addressed to all men, to Jews and Gentiles alike (Matthew 28:19; Mark 16:15; Romans 9:24-25). But this universal call is not inseparably connected with salvation, although it leaves all to whom it comes inexcusable if they reject it (John 3:14-19; Matthew 22:14).
An effectual call is something more than the outward message of the Word of God to men. It is internal, and is the result of the enlightening and sanctifying influence of the Holy Spirit (John 16:14; Acts 26:18; John 6:44), effectually drawing men to Christ, and disposing and enabling them to receive the truth (John 6:45; Acts 16:14; Ephesians 1:17).