Why does the love of Christ constrain us?
The love of Christ constrains and drives believers because they conclude that if one died for all, then all were spiritually dead. He died for all so that those who live should no longer live for themselves but for Him who died and rose again.
Les teaches from 2 Corinthians 5:14–15 that the love of Christ constraineth us—it drives us—because we thus judge, or conclude, that if one died for all, that is for every human being, then every human being was spiritually dead. Verse 15 adds that He died for all, that they who live should not henceforth live unto themselves, but unto Him who died for them and rose again. Les points out that this is the Gospel, and it just keeps popping up all the time. The surrounding context stresses that Scripture must speak for itself: don't go by what I say, go by what the Book says.
For the love of Christ constraineth us; because we thus judge, that if one died for all, then were all dead: