Translation:

248. And (further) their Prophet said to them: "A sign of his authority is that there shall come to you the Ark of the Covenant with (an assurance) therein of security from your Lord and the relics left by the family of Moses and the family of Aaron carried by angels. In this is a Symbol for you if ye indeed have faith."

Notes (Tafseer)

281. Ark of the Covenant: Tabut: a chest of acacia wood covered and lined with pure gold, about 6ft x 3ft x 3ft. See Exod xxv. 10-22. It was to contain the "testimony of God", or the Ten Commandments engraved on stone, with relics of Moses and Aaron. Its Gold lid was to be the "Mercy Seat" with two cherubims of beaten gold, with wings oustretched. This was a sacred possession to Israel. It was lost to the enemy in the early part of Samuel's ministry; see n. 278 to ii. 246; when it came back, it remained in a village for twenty years and was apparently taken to the capital when kingship was instituted. It thus became a symbol of unity and authority.

282. Security: sakina-safety, tranquility, peace. Later Jewish writings use the same word for a symbol of God's Glory in the Tabernacle or tent in which the Ark was kept, or in the Temple when it was built by Solomon.

283. Carried by angels: these words refer to the Tabut or Ark, the cherubims with outstretched wings on the lid may well be supposed to carry the security or peace which the Ark symbolised.