In speaking of Bible imagery, we must beware of straining the figures employed, and forcing upon them an interpretation which is beyond their natural meaning.
The text does not compare the light of the Christian with the light of the sun, but simply the Christian with the going forth of the sun.
The analogy then leads us to speak, in the first place, of the progressive nature of the Christian’s life—his constant upward advancement.
The sun is ever going forth. There is no pause nor cessation to his movements. Tempests and storms sweep over us, and calms succeed; changes and revolutions mark every thing here on earth, but the sun stops not in his career. His work is never done.
Even so is the Christian life—an onward movement, an advancement step by step in the work of grace.
As Christians, there is no such thing as our standing still, or resting satisfied with our present attainments in knowledge and holiness. It is this onward impulse, this disposition to push forward, this ardent longing for increasing grace, which is one of the strongest evidences that we are truly Christians. Hypocrites and self-deceived ones occasionally are susceptible of religious emotion. Hypocrites may join the church, and stay there till they die, and yet feel no need of progress. But where grace is truly felt, it causes the believer to long for more. The least conformity to the divine image begets a desire for more holiness. It can be satisfied only by awaking in his likeness. “Not as though I had already attained,” “I count not myself to have apprehended,” is the sentiment of every true Christian soul. “I press towards the mark for the prize of the high calling of God in Christ Jesus,” is the fixed purpose of every believer.
The Christian’s efforts in grace are not self-exhausting, but self-invigorating. The more he runs, the swifter of foot is he. The duties of yesterday never weary his strength for to-day.
Would you test your piety? then look not back in the distance of years to find the evidences of your salvation. But look at the passing weeks and months, to trace along their history the workings of divine grace. And Oh, let me warn you that you are trusting in a false and empty hope, unless there be found in your experience a growing conformity to Christ your Saviour, a series of conquests over temptations and besetting sins, a steadier fidelity in Christian duty, a deeper spirituality, a giving way of carnal lusts, a stronger faith, a brighter hope, and a nearer anticipation of heaven and glory. For if you are indeed a Christian, there will be found in you an onward progress in a holy life, a moving forward towards perfection, which will justify us in comparing it to the going forth of the sun.
Again, a Christian life is like the going forth of the sun, inasmuch as it is a progress involving a mighty power. The text speaks of the sun going forth in his might. The psalmist also describes him, “rejoicing as a strong man to run a race.” The apparent motion of the sun daily through the heavens, suggests the idea of almighty power. As if conscious of his strength, he strides like a giant across the sky.
So is the Christian’s progress in a holy life one which involves an outlay of exhaustless energies.