Allah stated that when He sent Adam, Hawwa', and Shaytan to earth from Paradise, He warned them that He will reveal Books and send Prophets and Messengers to them, i.e., to their offspring. Abu Al-`Aliyah said, "Al-Huda, refers to the Prophets, Messengers, the clear signs and plain explanation."

فَمَن تَبِعَ هُدَايَ

(And whoever follows My guidance) meaning, whoever accepts what is contained in My Books and what I send the Messengers with,

Descension of Adam was not a punishment

That is why the command for Adam (علیہ السلام) to go down to the earth was not withdrawn even when he had been pardoned: only the mode was now altered. Earlier the command had been given in the mode of authority, and the sending down to the earth intended as a punishment: hence the reference to the enmity among men. Now, it was in the mode of wisdom, and the sending down to the earth, an honour - the honour of vice regency. Hence the reference to things Viceregency involves. In commanding Adam and Hawwa (علیہما السلام) and their progeny to live on the earth, Allah told them that He would be sending down to men His guidance - that is, the injunctions of the Shari'ah - through revelation, and that those who follow it faithfully shall be free from sorrow and anxiety - in other words, they shall not have to grieve about any loss in the past, nor to worry about some misfortune in the future.