And thou shalt put into the ark the {f} testimony which I shall give thee.

(f) The stone tables, the rod of Aaron and manna which were a testimony of God's presence.

Jamieson-Fausset-Brown Bible Commentary

16. the testimony-that is, the two tables of stone, containing the ten commandments, and called "the testimony," because by it God did testify His sovereign authority over Israel as His people, His selection of them as the guardians of His will and worship, and His displeasure in the event of their transgressing His laws; while on their part, by receiving and depositing this law in its appointed place, they testified their acknowledgment of God's right to rule over them, and their submission to the authority of His law. The superb and elaborate style of the ark that contained "the testimony" was emblematic of the great treasure it held; in other words, the incomparable value and excellence of the Word of God, while its being placed in this chest further showed the great care which God has ever taken for preserving it.

Matthew Henry's Concise Commentary

25:10-22 The ark was a chest, overlaid with gold, in which the two tables of the law were to be kept. These tables are called the testimony; God in them testified his will. This law was a testimony to the Israelites, to direct them in their duty, and would be a testimony against them, if they transgressed. This ark was placed in the holy of holies; the blood of the sacrifices was sprinkled, and the incense burned, before it, by the high priest; and above it appeared the visible glory, which was the symbol of the Divine presence. This was a type of Christ in his sinless nature, which saw no corruption, in personal union with his Divine nature, atoning for our sins against it, by his death. The cherubim of gold looked one towards another, and both looked downward toward the ark. It denotes the angels' attendance on the Redeemer, their readiness to do his will, their presence in the assemblies of saints, and their desire to look into the mysteries of the gospel. It was covered with a covering of gold, called the mercy-seat. God is said to dwell, or sit between the cherubim, on the mercy-seat. There he would give his law, and hear supplicants, as a prince on his throne.