(Ta'dhdhana) means 'declared', according to Mujahid, or 'ordained', according to others. This part of the Ayah indicates a vow,

(that He will keep on sending against them) against the Jews,

(till the Day of Resurrection, those who would afflict them with a humiliating torment.) on account of their disobedience, defying Allah's orders and Law and using tricks to transgress the prohibitions. It was reported that Musa required the Jews to pay the production tax for seven or thirteen years, and he was the first to do so. Also, the Jews fell under the humiliating rule of the Greek Kushdanin, Chaldeans and later on the Christians, who subjugated and disgraced them, and required them to pay the Jizyah (tribute tax). When Islam came and Muhammad ﷺ was sent, they became under his power and had to pay the Jizyah, as well. Therefore, the humiliating torment mentioned here includes disgrace and paying the Jizyah, as Al-'Awfi narrated from Ibn 'Abbas. In the future, the Jews will support the Dajjal (False Messiah); and the Muslims, along with 'Isa, son of Mary, will kill the Jews. This will occur just before the end of this world. Allah said next,

(Verily, your Lord is quick in retribution), with those who disobey Him and defy His Law,

(and certainly He is Oft-Forgiving, Most Merciful.) for those who repent and go back to Him. This Ayah mentions both the mercy, as well as, the punishment, so that no despair is felt. Allah often mentions encouragement and warning together, so that hearts always have a sense of hope and fear.