The ark was the throne of Yahweh where He dwelt in a localized way and met with the Israelites through their high priest. It was the seat of His sovereignty but also the place where He met with His people (v. 22). This is why directions for its construction come first. The testimony (Ten Commandments, vv. 16, 22) lay inside the ark, which was a box. God's dwelling among His people and His relationship with them thus quite literally rested on the Ten Commandments. The mercy seat (v. 17) was the "lid"of this box and was solid gold. It was there that the high priest offered sacrificial blood once a year to atone for (cover) the sins of the Israelites as a nation. This offering made propitiation (satisfaction) for their sins for one year (cf. Lev. 16).
The Greek word used to translate "mercy seat"here in the Septuagint (hilasterion) is essentially the same word used to describe Jesus Christ as our propitiation in 1 John 2:2 (hilasmos). The mercy seat was for the Israelites temporarily what Jesus Christ is for all people permanently: the place where God found satisfaction.
"It [mercy] is a sweet word! A seat of mercy, baptised [sic] in mercy, from which mercy flows forth. Not wrath, not judgment, not indignation, but mercy is pouring forth from its original fountain in the heart of God."443
The cherubim (v. 18) were angels who "apparently have to do with the holiness of God as violated by sin."444They may have looked like winged human-headed lions.445Josephus wrote that Moses saw these creatures around God's throne when he was on Mt. Sinai.446