Outward and Inward Calls

Here is a brief summary presented by Thomas Paul Simmons in his work "A Systematic Study of Bible Doctrine"
THE OUTWARD AND INWARD CALLS OF GOD
I. THE OUTWARD CALL
The Scripture clearly speaks of two different calls. The first one in the order of occurrence is known generally as the outward or external call. The following Scriptures refer to this call: Isa. 45:22; 55:6; Matt. 9:13; 11:28; 22:14; Mark 2:17; Luke 5:32; Rev. 22:17. There are other Scriptures that evidently refer to both calls. These are reserved until we take up the inward call.
The outward call is through the preaching of the gospel. It was by means of the gospel that Jesus called sinners to repentance. Today every presentation of the gospel is a call to men to forsake sin and trust Christ. The preaching of the gospel is also properly attended by a setting forth of man's need of salvation and of his duty and responsibility under God to repent and believe (Acts 17:30). There should also be the earnest entreaty to men to be reconciled to God (2 Cor. 5:20) and an invitation to all that labor (Matt. 11:28), and are athirst (Isa. 55:1; John 7:37; Rev. 22:17).
This call is therefore general. By this we mean that it is not confined to the elect (Matt. 22:14). We are commanded to preach the gospel to all. This call is intended for all men, though all do not hear it. This is true just as all men are commanded to repent (Acts 17:30), even though all men do not hear this command.
This call, of itself, is always ineffective. To Israel God said: "When I called, ye did not answer" (Isa. 65:12). The call referred to here was an outward call similar to the call now under discussion. Because of man's depravity, the preaching of the gospel alone is never sufficient to bring him to Christ. He needs more than an outward call. The gospel "is the power of God unto salvation to every one that believeth" (Rom. 1:16); but "the natural man receiveth not the things of the Spirit of God; for they are foolishness unto him, and he cannot know them, because they are spiritually judged" (1 Cor. 2:14). Man must be enabled to turn from sin and believe on Christ. Jer. 13:23; John 12:39, 40; 6:44, 65.
Nevertheless it is the immediate duty of all to accept this call. Acts 17:30.
II. THE INWARD CALL
The following Scriptures refer to the inward call: Acts 2:39; Rom. 1:6; 8.28, 30; 9:11,24; 1 Cor. 1:1,26; 7:15; Gal. 1:15; 5:8; Eph. 4:4; Col. 3:15; 1 Thess. 5:24; 2 Thess. 2:14; 2 Tim. 1:9; Heb. 9:15; 1 Pet. 1.15; 2:9; 3:9; 5:10; 2 Pet. 1:3,10; Jude 1. Some of these Scriptures, as has been indicated already, seem to allude to both the inward and outward call.
The inward call is a direct call through the Spirit. The Holy Spirit takes the preached gospel and opening the heart of the sinner (Acts 16:14), applies the word to the heart in regenerating power. It is then, and only then, that man is able to understand and receive the things of the Spirit of God. Thus the inward call is also through the gospel, but it is through the gospel as applied by the Holy Spirit. The Scriptures touching on this work of the Spirit through the word will be given when we study regeneration.
This call is particular. By means of it the chosen objects of God's saving grace are singled out. The difference here between the outward and the inward calls may be imperfectly illustrated by the difference between a general invitation extended by a church to the people of a community to attend its services and the personal invitations that are extended to particular individuals by the membership of the church. Of course, as we have said, this only imperfectly illustrates the difference between God's two calls. Rom. 8:30 shows the particularity of this call.
This call is always effective. It is manifest that the Scriptures given at the beginning of the discussion of this call refer to an effective and efficient call. This call is never resisted; yet, in responding to it, man acts voluntarily and freely. See chapter on "The Free Agency of Man." The effectiveness of this call is shown by Rom. 8:28, 30; 1 Cor. 1:24.