A.B. Simpson emphasizes the significance of the doctrine of the Lord's coming in his sermon on Thessalonians Chapter 1, highlighting it as a central theme that motivates conversion, faithful ministry, and Christian love. He explains that the anticipation of Christ's return serves as a source of comfort for the afflicted and a call to watchfulness for believers, urging them to live in holiness and readiness. Simpson also warns against the apostasy that may precede the Lord's return, encouraging believers to remain steadfast in their faith and duties while awaiting His coming.