Salamun Alaikum.
The immediate address has to be appreciated which are those recipients who were hearing the message of the Quran directly. They were being instructed to obey the messenger in not only his capacity as a spiritual leader but also in his capacity as a leader of the new Islamic state. He taught and guided from the Quran, he distributed alms, booty, acted as judge etc.
In the verse you quote, it is clear that the Prophet was a living entity amongst his people making use of the Quran for guidance to address his present day affairs. After his death, we must follow what was inspired in him and left for the Ummah.
What was left for the ummah was the Quran. Secondary sources such as Ahadith were not canonised until centuries after the death of the Prophet. No direct companion including any immediate main caliph of Islam ever sought to leave a book of Hadith in their name with their own hands nor did they ever oversee such a collection or project. What we have in their names are narrations compiled by later compilers centuries removed under the influence of powerful dynasties such as the Abbasids. This is not contemporaneous evidence but a source of literature based on faith of transmission and the transmitters.
If the Prophet made use of the Quran to make His decisions, then we must follow in his footsteps and make use of the Quran as the bedrock of our society and from which our governance and guidance emanates.
The prophet applied the timeless Quran to his time specific period of 7th century Arabia. Today, we must apply the timeless Quran and the guidance within our lives today.
I hope that helps, God willing.
Regards,
Joseph.