[4:144] O you who believe, take not the disbelievers as friends instead of the believers: do you desire to give God over you a clear warrant?
He repeated the admonition to them and confirmed the command to part from the enemies so as to emphasize the warning, intensify the rebuke, and to end the argument by putting a stop to any possible excuses.
Do you desire to give God over you a clear warrant?: He warned them about their friendship with the disbelievers over and above other oppositional acts because it involves a preference for something other than the appropriate object of adoration (maʿbūd). Preferring another to the beloved (maḥbūb) is the gravest of sins in the precepts of love. When one's heart becomes engaged with others in the place reserved for believers, this necessarily brings about a bad outcome. How can one's heart be engaged with others in the place reserved for the Real?
The punishment He promised them is leaving them to their own devices and what they have chosen in siding with the disbelievers. What a wretched substitution! It is the same with those who hold back from the Real (ḥaqq) - He leaves them with that which is created (khalq), which doubles their affliction. Both of these are severe punishments.