Verse 4:25 from Sahih International. All translations say the exact same but this one is worded better:
"And whoever among you cannot [find] the means to marry free, believing women, then [he may marry] from those whom your right hands possess of believing slave girls. And Allah is most knowing about your faith. You [believers] are of one another."
Allah knows about our faith. He then says in verse 5:3 (Sahih)
"This day I have perfected for you your religion and completed My favor upon you and have approved for you Islam as religion."
Question: Why is Allah SWT telling us to marry Muslims? If not free, then believing slaves? Note: This verse applies to women as well. He also says that he knows about our faith. He says islam is our religion. He also says that the believers are one of another.
Verse 9:71 from Sahih International, Muhsin Khan, Pickthall, Yusuf Ali, and Shakir:
The believing men and believing women are allies of one another. They enjoin what is right and forbid what is wrong and establish prayer and give zakah and obey Allah and His Messenger. Those - Allah will have mercy upon them. Indeed, Allah is Exalted in Might and Wise.
"The believers, men and women, are Auliya' (helpers, supporters, friends, protectors) of one another, they enjoin (on the people) Al-Ma'ruf (i.e. Islamic Monotheism and all that Islam orders one to do), and forbid (people) from Al-Munkar (i.e. polytheism and disbelief of all kinds, and all that Islam has forbidden); they perform As-Salat (Iqamat-as-Salat) and give the Zakat, and obey Allah and His Messenger. Allah will have His Mercy on them. Surely Allah is All-Mighty, All-Wise. "
"And the believers, men and women, are protecting friends one of another; they enjoin the right and forbid the wrong, and they establish worship and they pay the poor-due, and they obey Allah and His messenger. As for these, Allah will have mercy on them. Lo! Allah is Mighty, Wise."
"The Believers, men and women, are protectors one of another: they enjoin what is just, and forbid what is evil: they observe regular prayers, practise regular charity, and obey Allah and His Messenger. On them will Allah pour His mercy: for Allah is Exalted in power, Wise."
"And (as for) the believing men and the believing women, they are guardians of each other; they enjoin good and forbid evil and keep up prayer and pay the poor-rate, and obey Allah and His Messenger; (as for) these, Allah will show mercy to them; surely Allah is Mighty, Wise."
And who exactly are these people? The Quran answers again:
Whoever works righteousness — whether male or female — while he (or she) is a true believer (of Islamic Monotheism) verily, to him We will give a good life (in this world with respect, contentment and lawful provision), and We shall pay them certainly a reward in proportion to the best of what they used to do (i.e. Paradise in the Hereafter)." (Quran 16:97)
"Lo! men who surrender unto Allah, and women who surrender, and men who believe and women who believe, and men who obey and women who obey, and men who speak the truth and women who speak the truth, and men who persevere (in righteousness) and women who persevere, and men who are humble and women who are humble, and men who give alms and women who give alms, and men who fast and women who fast, and men who guard their modesty and women who guard (their modesty), and men who remember Allah much and women who remember - Allah hath prepared for them forgiveness and a vast reward." (Quran 33:35)
So, as we can see, the believing men and women are allies, protectors and guardians of each other. When Allah SWT stated Islam is the religion, then what makes up those who follow islam? It's the above verse. Clearly, connections can be seen from all of these verses. Which has to mean that verse 5:5, where man say it speaks of interfaith marriages, has to mean something else.