Imam Sadiq (peace be upon him): It is narrated from Abu Amr al-Zubayri: I said to Imam Sadiq (peace be upon him), "Does iman (faith) have degrees and ranks, in which the believers surpass one another before Allah?" He said, "Yes!" I said, "May Allah have mercy on you! Explain it to me so that I may understand." He said, "Allah has set up a race among the believers, just as horses are raced against each other on the day of racing, and He has given them merit according to their rank in racing towards Allah. He placed the affairs of each of the believers according to the degree of his precedence, and did not diminish his right from that degree. None of those who fell behind him [in this race] can outstrip him, and no one of lesser merit can precede one of greater merit. It is by this that the earlier and later ones of this ummah surpass one another." I said, "Tell me of a word by whose content Allah the Mighty and Majestic has encouraged the believers to race in faith." He said, "The word of Allah the Mighty and Majestic: 'Race with one another to attain forgiveness from your Lord and a Paradise the breadth of which is like the breadth of the heavens and the earth. It has been prepared for those who believe in Allah and His messengers.' (al-Hadid/21)." Then he recalled the verse in which Allah the Mighty and Majestic gave His friends merit over one another, and said: We gave some of those messengers merit over others; among them was one to whom Allah spoke, and some He raised in degrees, and We gave Isa son of Maryam clear signs and supported him with the Holy Spirit [but the merit and rank of those prophets did not prevent the disputes of the ummahs]. And if Allah had willed, those who came after them would not have fought after all the clear signs that came to them [but Allah did not compel people and left them free to tread the path of felicity], but these ummahs disputed among themselves — some believed and some disbelieved [and war and bloodshed broke out. And again], if Allah had willed, they would not have fought each other, but Allah does whatever He wills [in accordance with wisdom, and compels no one to accept anything]. (al-Baqarah/253) وَ یُؤْتِ کُلَّ ذِی فَضْلٍ فَضْلَهُ وَ إِنْ تَوَلَّوْا فَإِنِّی أَخافُ عَلَیْکُمْ عَذابَ یَوْمٍ کَبیر [And He grants every possessor of merit his merit, and if you turn away, indeed I fear for you the punishment of a great day].