Because of their breaking the covenant, and of their rejecting the Ayat (proofs, evidences, verses, lessons, signs, revelations, etc.) of Allah, and of their killing the Prophets unjustly, and of their saying: "Our hearts are wrapped (with coverings, i.e. we do not understand what the Messengers say)" - nay, Allah has set a seal upon their hearts because of their disbelief, so they believe not but a little.