In the Name of Allah, the Most Gracious, the Most Merciful.
The Success is for the believers whose qualities are described here
قَدْ أَفْلَحَ الْمُؤْمِنُونَ
(Successful indeed are the believers) means, they have attained victory and are blessed, for they have succeeded. These are the believers who have the following characteristics:
الَّذِينَ هُمْ فِى صَلاَتِهِمْ خَـشِعُونَ
(Those who with their Salah are Khashi`un.) `Ali bin Abi Talhah reported that Ibn `Abbas said:
خَـشِعُونَ
"(Khashi`un) means those with fear and with tranquillity." This was also narrated from Mujahid, Al-Hasan, Qatadah and Az-Zuhri. It was reported from `Ali bin Abi Talib, may Allah be pleased with him, that Khushu` means the Khushu` of the heart. This was also the view of Ibrahim An-Nakha`i. Al-Hasan Al-Basri said, "Their Khushu` was in their hearts." So they lowered their gaze and were humble towards others. Khushu` in prayer is only attained by the one who has emptied his heart totally, who does not pay attention to anything else besides it, and who prefers it above all else. At that point it becomes a delight and a joy for eyes, as in the Hadith recorded by Imam Ahmad and An-Nasa'i from Anas, who said that the Messenger of Allah ﷺ said:
Those are the inheritors who will inherit Firdaus (Paradise) - 23:10, 11.
The good Muslims who possess the attributes described above have been declared in this verse to be the heirs to the garden of Paradise. There is a suggestion here that just as the assets of a deceased person must devolve on his heirs, similarly the possessors of these attributes will, without doubt, enter Paradise. It should be noted that the possessors of these seven qualities have been mentioned in the beginning as those who attain falah or success, then after describing these qualities it is mentioned in this last sentence that possessors of these qualities will inherit Paradise. This indicates that the total falah (success) may be achieved in Paradise only.
Tazkirul Quran
Maulana Wahiduddin KhanOn ayahs 11–13
In this world of God, success is for one who is a true believer, one who devotes himself fully to God and not to anybody other than God, and who leads a God-oriented life. Realisation of God is not a simple matter. It brings about a revolution in the life of a man. He becomes a worshipper of God and bows down before Him in submission. His sincerity and seriousness increase to the extent that wasting time in useless pursuits appears fatal to him. He sets aside a portion of his earnings in the name of God and with that he helps the needy. He exercises control over his sexual desires and gives free rein to them only within the limit prescribed by God for the purpose. He lives his life in this world as a responsible person and never misappropriates whatever is entrusted to him. Such a man never dishonours any pledge undertaken by him. Those who possess these qualities are the favoured subjects of God. These are the people for whom God has kept ready the ideal world, namely, the gardens of Paradise. After death they will be sent into this sublime atmosphere so that they may savour its joys forever.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.
