In “Image” no. 182, Edwards compares lengthy prosperity with long summertimes which allow “flies and other insects that are hurtful and noisome” and other pestilence to breed unrestrained.
So a long continuance of a summer of prosperity, of outward or spiritual comforts, breeds hurtful and noisome and corrupting insects as it were in the soul. Many evil things, contrary to the humility and simplicity that is in Christ, gradually creep in till they swarm.
Sharp winter seasons of humiliation are necessary in order to kill the sinful inclinations of the soul so that sanctification may progress. A cold snap or “a small frost may chill ’em and restrain ’em,” but it takes a long, hard winter to destroy them. This is true for individuals and churches.