Translation:

5. And remember Moses said to his people: "O my people! why do ye vex and insult me though ye know that I am the apostle of Allah (sent) to you?" Then when they went wrong Allah let their hearts go wrong: for Allah guides not those who are rebellious transgressors.

Notes (Tafseer)

5434. The people of Moses often rebelled against him, vexed his spirit, and insulted him. See xxxiii. 69, n. 3774, and (in the Old Testament) Num xii. 1-13. They did it not through ignorance, but from a selfish, perverse, and rebellious spirit, for which they received punishment. The Ummat of Islam should remember and take note of it, and should avoid any deviation from the Law and Will of Allah.

5435. The sinner's own will deviates, i.e., goes off from the right way, and he does wrong. That means that he shuts off Allah's grace. Allah then, after his repeated rebellion, withdraws the protecting Grace from him, and the sinner's heart is tainted: there is "a disease in his heart", which is the centre of his being: his spiritual state is ruined. Allah's guidance is withdrawn from him.