Charles H. Spurgeon on Psalms 119:2

Testimonies. The notion by which the word of God is expressed is "testimonies"; whereby is intended the whole declaration of God's will in doctrines, commands, examples, threatenings, promises. The whole word is the testimony which God hath deposed for the satisfaction of the world about the way of their salvation. Now because the word of God branches itself into two parts, the law and the gospel, this notion may be applied to both. First, to the law, in regard whereof the ark was called "the ark of the testimony" (Exodus 25:16), because the two tables were laid up in it. The gospel is also called the testimony, "the testimony of God concerning his Son." "To the law, and to the testimony" (Isaiah 8:20); where testimony seems to be distinguished from the law. The gospel is so called, because therein God hath testified how a man shall be pardoned, reconciled to God, and obtain a right to eternal life. We need a testimony in this case, because it is more unknown to us. The law was written upon the heart, but the gospel is a stranger. Natural light will discern something of the law, and pry into matters which are of a moral strain and concernment; but evangelical truths are a mystery, and depend upon the mere testimony of God concerning his Son. Thomas Manton.