Dear noble brothers, we are discussing a new lesson of this series about the Ayaat that start with, "O you who believe…", and the Ayah today is the following:  

(O you who believe! Be afraid of Allah and give up what remains (due to you) from Riba (usury) (from now onward), if you are (really) believers.)

[Al-Baqarah, 248]

The Quran contains many Ayaat about Riba (usury):  

There are many Ayaat in the Noble Quran which are about Riba (usury), and the way it is mentioned is really terrifying:   

(Those who eat Riba (usury) will not stand (on the Day of Resurrection) except like the standing of a person beaten by Shaitan (Satan) leading him to insanity. That is because they say: "Trading is only like Riba (usury),"...)

[Al-Baqarah, 275]

Why should be there a difference between investing your money in a firm and in a bank? The answer is that in a bank man can gain constant profits while he is relaxing, but in the firm, the profits are changeable. Well, if someone invests his money with a business man, and the latter tells him that he will give him constant profits, then this is definitely Riba.  

(Those who eat Riba (usury) will not stand (on the Day of Resurrection) except like the standing of a person beaten by Shaitan (Satan) leading him to insanity. That is because they say: "Trading is only like Riba (usury)," whereas Allah has permitted trading and forbidden Riba (usury). So whosoever receives an admonition from his Lord and stops eating Riba (usury) shall not be punished for the past; his case is for Allah (to judge); but whoever returns [to Riba (usury)], such are the dwellers of the Fire – they will abide therein.)

[Al-Baqarah, 275]

Allah the Almighty says: 

(Allah will destroy Riba (usury) and will give increase for Sadaqat (deeds of charity, alms, etc.) And Allah likes not the disbelievers, sinners.)

[Al-Baqarah, 276]

Allah the Almighty threatens those who deal with Riba with war from Him. In fact,[ ] the only two kinds of people who are threatened with war from Allah, Exalted and Sublime be He, are: First, those who easn Riba as mentioned in the aforementioned Ayah: 

(And if you do not do it, then take a notice of war from Allah and His Messenger but if you repent, you shall have your capital sums. Deal not unjustly (by asking more than your capital sums), and you shall not be dealt with unjustly (by receiving less than your capital sums).)

[Al-Baqarah, 279]

Second: those who treat Allah's Awliya' (the true devoted believers of Allah) with hostility and enmity. In this regard, pay attention to the following Hadith, please:

(On the authority of Abu Hurairah (may Allah be pleased with him) who said: The Messenger of Allah (peace and blessings of Allah be upon him) said, "Verily Allah the Almighty has said: 'Whosoever shows enmity to a wali (friend) of Mine, then I have declared war against him…'")

[Al-Bukhari]