One of the most important things about right division is that it enables us to understand and clearly present the only gospel by which sinners are saved in this present age of grace. The "word of truth" (2 Tim. 2:15) can refer to the scripture in general (Ps. 119:43; 2 Cor. 6:7), or to the gospel in particular.
The gospel of the grace of God is "the word of truth" by which we are saved today (Eph. 1:13), but the gospel of the kingdom is "the word of truth" by which Israel will be saved in the future (Jam. 1:18). Failure to rightly divide these messages leads to confusion and false doctrine.
Let's compare the word of truth in Ephesians with the word of truth in James.
1. Paul wrote to those who were uncircumcised Gentiles (Eph. 2:11-12), but James wrote to the twelve tribes of Israel (Jam. 1:1).
2. The gospel that Paul preached had to do with a mystery hid from the prophets (Eph. 3:1-6; 6:19-20), but the gospel Peter, James, and John preached was a prophesied message (1 Pet. 1:9-13; 23-25).
3. Paul taught that salvation is by faith alone (Eph. 2:8-9, justification by the faith OF Christ), but James taught that a man is not justified until he proves his faith by his works (Jam. 1:21-27; 2:14-26).
4. Paul taught that believers are sealed with the Spirit the moment they believe the gospel (Eph. 1:13-14; 4:30 = eternal security), but James taught that believers must endure faithfully to the end (Jam. 1:12; 5:7-11).
Things that are different are not the same!