Watson, in volume four of his book on Revelations, which was based on the commentary of Dr. Benson, remarks that the fact that Luke’s writing is not inspired is evident from the dedication of his Gospel to Theophilus:

 For as much as many have taken in hand to set forth in order a declaration of those things which are most surely believed among us, even as they delivered them unto us, which from the beginning were eyewitnesses, and ministers of the word; it seemed good to me also, having had perfect understanding of all things from the very first, to write unto thee in order, most excellent Theophilus, that thou mightest know the certainty of those things, wherein thou hast been instructed. [1]

Waston says about this:

The ancient writers of Christian theology have also given a similar opinion. Irenaeus said that Luke conveyed to us the things which he learnt from the apostles. Jerome said that Luke does not depend only on Paul, who was never in the physical company of Christ.  Luke also acquired the knowledge of the Evangel from other apostles as well.

He further elucidates:

The apostles, when they used to speak or write anything concerning the faith, were protected with the treasure of inspiration that they had. Being, however, human beings, and men of reason and inspiration, they were just like other people when describing common events.

This made it possible for Paul to write in his first epistle to Timothy, without inspiration:

Drink no longer water, but use a little wine for thy stomach’s sake and thine often infirmities.[2]

and further:

          The cloak that I left at Troas with Carpus, when thou comest, bring with thee, and the books, but especially the parchments. [3]

          And that he could write to Philemon, “But withal prepare me also a lodging.” (v.22) And as he wrote to Timothy, "Erastus abode at Corinth; but Trophimus have I left at Miletum sick.” [4]

          However there are other occasions when it is clear that Paul speaks by inspiration, as in his first letter to the Corinthians:

          And unto the married I command, yet not I, but the Lord, Let the wife depart from her husband. [5]

          But in verse twelve of the same epistle he says:

          But to the rest speak I, not the Lord.

          Then in verse twenty-five he says:

          Now concerning virgins I have no commandment of the Lord: yet I give my judgment, as one that hath obtained mercy of the Lord to be faithful.

          The book of Acts contains this statement:

          Now when they had gone throughout Phrygia and the region of Galatia, and were forbidden of the Holy Ghost to preach the word in Asia. After they were come to Mysia, they assayed to go into Bithynia: but the Spirit suffered them not.

          From the above we are given to understand that the apostles’ work was based on two things: reason and inspiration. They used the first to speak of general events, while through the other they gave religious instructions related to the Christian faith. This is why the apostles, like other human beings, committed mistakes in their domestic affairs and in their intentions. This is quite evident from Acts 23:3; Rom. 15:24,28; I Cor. 16:5,6,8 and 2-Cor. 11:15-18.

          The nineteenth volume of the Rees Encyclopedia contains this description under the entry ”Dr. Benson”:

          Whatever he has written in connection with inspiration seems to be clear and logical and, indeed, unique in its application.

[1]  Luke 1:1-4.

[2] I Tim. 5: 23.                 [2]  2 Tim 4:13.     [2] 2 Tim. 4:20.                 [2]1 Cor. 7:10.     Acts 16:6,7.