Allah (SWT) had appointed 40 days and nights for Musa (PBH) to receive the code of conduct for Bani Israel in the form of laws which distinguished right from wrong. In his absence, on the advice of a person named Samiri, Bani Israel moulded a calf out of their ornaments and started worshipping it. Musa (PBH) on his return got very angry and asked them to turn to Allah (SWT) for forgiveness by invoking Him through His Attribute ‘Al Bari’ meaning ‘One Who purifies’i.e. One who removes something unwanted and impure from something of utility and purity, so that He remove the evil of calf worship from them. There appears to be a hint here that Allah (SWT) should be invoked through the Attribute concerned with the subject of help sought, for example if one needs food he should invoke Allah (SWT) by His Attribute ‘AR Razzak’meaning ‘The Provider’, (Chapter: 7 Verse 180). Further as a punishment for their calf worship which amounts to polytheism, Musa (PBH) ordered them to kill themselves for their grave injustice, probably because murder is a lesser sin than polytheism which is unforgivable (Chapter: 4 Verses: 48, 116). Allah (SWT) is the Accepter of repentance, the Merciful, He therefore turned to them mercifully and pardoned them so that they should be grateful.”