I have studied Darby and a few other dispensationalists. I think they get “dividing the Word” right for correctly interpreting prophecy. No where did I see Darby or Walvoord, Ryrie and others (maybe Chaefer) “divide” the Age of Grace between two plans of Salvation.
I know Darby and many dispensationalists to include Ryrie get accused by many of doing just that “divid the gospel message.” They all deny it (maybe not Chaefer) and I believe them.
The age of grace ends at the rapture.
Paul's first six Epistles (1 and 2 Thess.; Gal.; 1 and 2 Cor.; and Rom.) are those whereby he went to the Jew first (Rom. 1:16 with Acts 13:5,14,46). He performed many miracles, signs and wonders (Acts 19:12) and legal ceremonies (Acts 16:3-4), ...."because of the Jews")(Acts 16:3) with (1 Cor. 9:20-23; 10:32).
Paul also had a ministry of revelation, preaching the unprophesied riches of Christ, the gospel of uncircumcision. The Church the body of Christ was GRADUAL in its growth. In Antioch, Acts 13:46 (45 A.D.), in Corinth, Acts 18:6 (54 A.D.0, and finally at Rome, Acts 28:27-28, (63 A.D.). HERE is where we see God making the transition from the Jewish age to the Church Age.
The Book of Acts is a transitional Book. From the kingdom age of believers to the body of believers, the Church the body of Christ. There is not a sudden poof, where one day it's one way, then it suddenly changes. It's a transition from Law to Grace. And Paul perfectly fits the person to receive the revelations of this from the risen Christ.