«And do not marry al-mushrikaat (idolatresses) till they believe (worship Allaah alone). And indeed a slave woman who believes is better than a (free) mushrikah (idolatress), even though she pleases you. And give not (your daughters) in marriage to al-mushrikun till they believe (in Allaah alone) and verily, a believing slave is better than a free mushrik (idolater), even though he pleases you. Those (al-mushrikun) invite you to the Fire, but Allaah invites (you) to Paradise and Forgiveness by His Leave, and makes His aayaat (proofs, evidences, verses, lessons, signs, revelations, etc.) clear to mankind that they may remember.»
Points of Explanation:
FIRST POINT: «And indeed a slave woman who believes is better than a (free) mushrikah (idolatress), even though she pleases you» meaning: she is better than a Christian or a Jew from one angle and she is better than a Buddhist or any type of polytheist from another angle.
Marriage to the believing woman is valid while marriage to the Buddhist and Hindu woman is invalid and it is obligatory to marry the believing woman verses the (general) polytheist woman. Whereas in the other situation, an exemption is made for Ahlul-Kitaab (the Jews and Christians). However, simply because the Jews and Christians have been exempted from this prohibition does NOT make them non-polytheists.
Some people think that a Jew and a Christian are not in actuality polytheists because Allaah has given us some special rulings with how to deal with them. This is an error. They are clear polytheists [due to the shirk they commit].
«And indeed a slave woman who believes is better than a (free) mushrikah (idolatress), even though she pleases you»
Marriage to a believing woman is better than a Jew or a Christian while both contracts are valid. And marriage to a believing woman is better than a Hindu or a Buddhist while the contract to the latter woman is invalid.
SECOND POINT: People are considered to be callers to what they are upon, whether they verbally or physically invite to their deen. Allaah says regarding them in a general manner:
«Those (al-mushrikun) invite you to the Fire.»
In his book Tafsīr al-Aayat al-Akhaam, Shaykh Muhammad ibn Saalih al-`Uthaymeen says that they are either calling to the Hell-Fire through explicit verbal invitation: "Worship others with Allaah," or "Stop worshiping Allaah alone" or they might invite you to the Hell-Fire with their actions and examples without a verbal invitation.
What about the believing woman? What is she inviting you to? What about the believing man? What is he inviting you to?
The opposite understanding is applied. The Muslim husband or the Muslim wife are going to invite you to Paradise, to Allaah, and to worshiping Him alone. Allaah says:
«But Allaah invites (you) to Paradise and Forgiveness by His Leave.»
Meaning: The mushrik invites you to the Hell-Fire and the Muslim will invite you to Allaah, and Allaah is the One leading you to Paradise. So it is the believer whose company will benefit you; the contract with them will benefit you, and the choice of a Muslim over a mushrik is a choice that will benefit you in the Hereafter, because you have as your close companion someone who is calling you to Allaah, either by their explicit invitation or by their example.
The mushrikeen are astray, they cannot ever guide you, and they would never be pleased in guiding you to something good because they themselves are astray. They do not know how to distinguish the good from evil. Allaah has described them saying:
«They are only like cattle; nay, they are even farther astray from the Path (i.e. even worse than cattle).»
Allaah further said:
«And who is more astray than one who calls (invokes) besides Allaah, such as will not answer him till the Day of Resurrection, and who are (even) unaware of their calls (invocations) to them?» 
They are astray and cannot offer guidance as they are astray themselves and they are leading others astray with their example and invitation. The believer, however, is the opposite of that. He is a caller to the truth, a caller to the way of Allaah, either through his action or direct invitation.
If every Muslim understands that every polytheist is upon ignorance and deviation and neglect and rejection of Allaah's order, what did Allaah mean when He said: «...even though she pleases you...»? Meaning: Their beauty can please you, their lineage, behavior, status or knowledge.
Abū Hurayrah (radiyallaahu `anhu) reported that the Messenger of Allaah (sallallaahu `alayhi wa sallam) said:
تنكح المرأة لأربع : لمالها ولحسبها وجمالها ولدينها((
«The women are married for four (reasons): her wealth, her noble lineage, her beauty, and her religion.»
Conversely, you can say that these are four reasons why women marry men as well. This advice is not restricted to the man looking for a woman, but for the woman who is looking for a man.
So then, what advice did the Messenger (sallallaahu `alayhi wa sallam) give us? Did he say: 'This is it, look for these four things and pick whichever one you want'? No, rather, he said:
))فاظفر بذات الدين تربت يداك((
«Seek the one with religion lest your hand be in dust.»
Some scholars commented said: «Lest your hands be in dust» meaning: lest you be a loser. Some scholars said it is further instruction for you to strive with utmost to marry the woman of religion and to be vigilant about it.
 Sūrah al-Baqarah (2):221
 Sūrah al-Furqaan (25):44
 Sūrah al-Ahqaaf (46):5
 Reported by Saheeh al-Bukhaaree no. 5090 from a hadeethof Abū Hurayrah (may Allaah be pleased with him).
 Fiqh of Marriage 2010, Class 01 ~ Choosing a Spouse, as explained by UstaathMūsá Richardson, hafidahullaah.