A quote from one writer on the subject:

According to the Bible the Lord “calls” or summons people to do certain things. In a general sense God calls all men to receive the salvation and redemption that can be found only in His Son Jesus Christ [Rom. 8:30; 1Cor. 1:9; 1Thes. 2:12]. This calling is more than just an invitation, though, it is a command [Acts 17:30]. Thus God calls and commands all men everywhere to repent and receive Christ. Though this calling is for all men, it is a call to the individual. God personally and individually invites and commands each individual to partake of the blessings of His redemption. This call is given outwardly by the gospel [2Thes. 2:14] and inwardly by the Holy Spirit [Rev. 22:17]. Those who refuse God’s gracious call will be eternally held accountable for their refusal [John 12:48].

After one has answered the call to salvation and received Christ, God calls him to other callings which are moral in mature and affect a believers attitude and conduct. He has called believers to “fellowship with Christ” [1Cor. 1:9], to “holiness” [1Thes. 4:7], to “liberty” [Gal. 5:13], to “peace” [1Cor. 7:15], and to “virtue” [2Pet. 1:3]. Believers are to “walk worthy” of the calling they have received [Eph. 4:1].

But there is still another calling that is even more personal. It is God’s call to the individual believer for a specific ministry. The Lord has been calling individuals for specific ministries for millennia. He called Abram out of Ur; Moses out of Egypt; and Aaron from among the Levites [Heb. 5:4]. God had certain duties He wanted them to perform. The Lord also called many others in the Bible for certain ministries. From Isaiah [Isa. 6:9] to the twelve disciples to Paul [1Tim. 1:11], the Lord has been calling men into His ministry.

A call from God into a ministry is a high and heavenly calling [Phil. 3:14] which, unfortunately, is taken lightly by some ministers today [if they are truly called]. Paul was called to be an “apostle,” “preacher,” and “teacher” of the Gentiles [Rom. 1:1; 1Tim. 1:1; etc.], and he never lost sight of his calling. He actively engaged in his ministry until the day his head was taken. Of course, the Lord doesn’t call men to be apostles today because no minister today has the “signs of an apostle” [2Cor. 12:12]. Church planters do this role today. I know there are some frauds out there who claim to be apostles but they are deceived. Just ask one of them for some signs and they usually shut up. But the Lord still calls men to other callings or vocations such as pastoring, evangelism, and teaching. He calls and provides these men to the Church for the “perfecting of the saints” [Eph. 4:11-12].