[2:9] They would deceive God and the believers; and only themselves they deceive; and they are not aware.
The harm of their deception and the punishment for it comes back to themselves, so it is as if they deceived themselves in actuality, for they but treated their own value lightly and belittled themselves. No one suffered the harm of their actions but themselves and they cut off their own lifeblood. When there is one who knows the true nature of things, the one who desires to deceive him only deceives himself.
The allusion in this verse is to the one who has forgotten His prior kindness. He says, 'mine, through me, from me and I', slandering in his delusion and conjecture [what should be] 'Yours, through You, from You, and You'. This delusion is the most difficult of punishments because he sees a mirage (sarāb) and thinks it is drink (sharāb) until he comes to it and finds it to be nothing, and he finds God there, Who pays him his account in full [24:39].