'Mercy seat' in the Bible

He it is whom God put forward as a Mercy-seat, rendered efficacious through faith in His blood, in order to demonstrate His righteousness-- because of the passing over, in God's forbearance, of the sins previously committed--

And above the ark were the Cherubim denoting God's glorious presence and overshadowing the Mercy-seat. But I cannot now speak about all these in detail.