Charles H. Spurgeon on Psalms 119:72

The law of thy mouth is better unto me. The sacred Scriptures are the treasures and pleasures of a gracious soul: to David they were better than thousands of gold and silver. A mountain of transparent pearls, heaped as high as heaven, is not so rich in treasure as these; hence that good man chose these as his heritage for ever, and rejoiced in them as in all riches. A covetous miser could not take such delight in his bags, nor a young heir in a large inheritance, as holy David did in God's word.

The word law comes from a root that signifies to try as merchants that search and prove the wares that they buy and lay up; hence also comes the word for gems and jewels that are tried, and found right. The sound Christian is the wise merchant, seeking goodly pearls; he tries what he reads or hears by the standard or touchstone of Scripture, and having found genuine truths he lays them up to the great enriching of this supreme and sovereign faculty of the understanding. Oliver Heywood.