If you want to judge how well a person understands the gospel, ask him what he makes of the death of Christ, and what the message of the cross is. The real Christian answers that while the message of the cross is foolishness to some and a stumbling block to others, to Christians it is the saving wisdom and power of God (1 Cor. 1:18-24). The confession of the real Christian is 'far be it from me to boast except in the cross of our Lord Jesus Christ, by which the world has been crucified to me and I to the world' (Gal. 6:14).
Sinclair Ferguson, in his Foreword to The Great Exchange: My Sin for His Righteousness, by Jerry Bridges and Bob Bevington, page 12.