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."
(And whoever follows My guidance) meaning, whoever accepts what is contained in My Books and what I send the Messengers with,
(There shall be no fear on them) regarding the Hereafter,
(nor shall they grieve) regarding the life of this world. Similarly, in Surat Ta Ha, Allah said,
(He (Allah) said: "Get you down (from the Paradise to the earth), both of you, together, some of you are an enemy to some others. Then if there comes to you guidance from Me, then whoever follows My guidance, he shall neither go astray, nor shall he be distressed.) (20:123)
Ibn `Abbas commented, "He will not be misguided in this life or miserable in the Hereafter." The Ayah,
(But whosoever turns away from My Reminder (i.e. neither believes in this Qur'an nor acts on its teachings) verily, for him is a life of hardship, and We shall raise him up blind on the Day of Resurrection.) (20:124) is similar to what Allah stated here,
(But those who disbelieve and belie Our Ayat ـ such are the dwellers of the Fire. They shall abide therein forever), meaning, they will remain in Hell for eternity and will not find a way out of it.