A wonderful little book by the man who influenced countless Puritan-minded pastors in his time. Being a bit repetitive at times, it served well as devotional literature to pair with daily Bible reading.
It is an extended reflection on Philippians 3:7-11 and, as such, draws out the Reformational views on justification by faith alone in Christ alone. Perkins would have us see Jesus, and in the light of his death and resurrection, come to see ourselves as sinners in need of grace. His concern is that plenty of people know about Christ but too few know Christ-personally, as Lord and Savior. For that reason, they continue in their sin with little concern to finish the race of faith well.
As Perkins drives home in the end of the book, the answer is not necessarily more effort; we can't "grip it and rip it" to salvation. Rather, we must constantly meditate on the costliness of our own sin, seeing even the smallest sin as the reason for the crucifixion, and bask in the glory of God's grace, love, and mercy toward us in Christ.