Dr. D. Martyn Lloyd-Jones:
What is the gospel? Well, you remember the answer of the Apostle Paul, ‘It is the power of God unto salvation to every one that believeth’ (Rom. 1.16).
How easy it is to forget that. How easy to preach it as a system, to preach it as a collection of ideas, or just to preach it as a truth. Ah, but you can do that without power. There are people, say the Apostle Paul, who ‘have a form of godliness, but deny the power thereof’ (2 Tim. 3.5).
Christianity is primarily a life. It is a power. It is a manifestation of energy.
–Martyn Lloyd-Jones, Revival (Crossway, 1987), 123
(HT: Dane Ortlund)