Al-walaa means loyalty and al-bara means disownment. In the context of Islam al-walaa is loyalty to Allah and whatever He is pleased with as well as friendship and closeness to the believers, whereas al-baraa is freeing oneself from that which is displeasing to Allah and disowning the disbelievers. After loving Allah and His Messenger (S Allah obligates us to love those who love Allah and His Messenger (S) and hate those who oppose Allah and His Messenger (S.). The Islamic Belief System('Aqeedah) obligates every Muslim to love the people of 'Tawheed and hate the people of Shirk. 
You will not find a people who believe in Allah and the Last Day having affection for those who oppose Allah and His Messenger, even if they were their fathers or their sons or their brothers or their kindred. Those - He has decreed within their hearts faith and supported them with spirit from Him. And We will admit them to gardens beneath which rivers flow, wherein they abide eternally. Allah is pleased with them, and they are pleased with Him - those are the party of Allah . Unquestionably, the party of Allah - they are the successful. Quran Surah Mujadilah 58 ayah 22
This ayah was revealed concerning the sahaabah, who either killed a relative in the Battle of Badr, or intended to. Abu Bakr had a disbelieving son (‘Abdur-Rahman) who afterward told his father, “I saw you but I avoided you (meaning because you are my father).” Abu Bakr said to him: “Had I seen you, I would not have avoided you.”
On the authority of Abu Hurrairah: The Messenger of Allaah (salallaahu 'alayhi wa sallam) said: Whoever would like to taste the sweetness of Eeman, then let him love a person - not loving him except for Allaah's sake. [Ahmad (2/298), al-Haakim (1/3 and 4/168); Isnaad is 'hasan']
On the authority of Abu Umaamah (radiallaahu ‘anhu) that the Messenger of Allaah (salallaahu ‘alayhi wa sallam) said: Man AHaba lillaah Wa Abghada lillaah Wa A’ta lillaah Wa Mana’ah lillaah Fa Qad Istakmal Al-Eeman (Whoever loves for the sake of Allaah, hates for the sake of Allaah, gives for the sake of Allaah, and prevents (withholds) for the sake of Allaah, has perfected Eeman.) [Abu Dawud (no. 4681), at-Tirmidhee (no. 2521), Ahmad (3/438, 440); 'Saheeh' due to witnesses, refer to al-Albaani's Al-Saheeha (no. 380)]
Shaykh As-Sa’dee (rahimahullaah), in his excellent work The Tree of Faith, said about this hadeeth:
“The place for love and hate is the heart, the place for giving and preventing [withholding] is the limbs. The single condition that encompasses all of these is sincerity, which is the spirit and essence of faith.
To love for the sake of Allaah means to love Allaah – to love what He loves of things such as actions, times, periods and circumstances, and to love those He loves such as the Prophets and their followers.
To hate for the sake of Allaah means to hate everything that Allaah hates of things such as disbelief, sin and transgression. It also means to hate those who commit these or call to these.
Giving includes the servant performing all that he has been enjoined to as mentioned in His saying [what means]: As for him who gives (in charity) and keeps his duty to Allaah and fears Him. And believes in Al-Husna. We will make smooth for him the path of ease (goodness). (Al-Layl, ayat 5-7)
This ayath refers to the slave giving everything he has been ordered with, not just property and wealth for this is but a portion of giving. The same applies to its opposite – preventing [withholding].
Through these four matters does the servant perfect his faith and religion
In the footnote related to this hadeeth is the following benefit relayed from Al-Manaawee’s work Faydul-Qadeer (6/38): “Some said that the reason that these matters perfect Eeman is that the religion revolves around four principles – two of which are internal, and two which are external.
The internal are love and hate, and the external are performing and abstaining. Hence, whoever’s intention becomes steadfast and firm, such that he loves, hates, performs and abstains for the sake of Allaah, has perfected the different stations of Eeman.”
On the authority of al-Baraa ibn 'Aazib (radiallaahu 'anhu): The Messenger of Allaah (salallaahu 'alayhi wa sallam) said: Awthaq 'Ural Eeman Al-Hubu fillaah wal-bughdu fillaah (The strongest handhold of Eeman is loving for Allaah's sake, and hating for Allaah's sake). [Ahmad (4/286), Ibn Abee Shaybah (no. 110); hasan due to supporting narrations]
Shaikh 'Abdul-'Aziz ibn 'Abdullaah ibn Baaz (rahimahullaah), in his work The Authentic Creed And The Invalidators of Islaam, said: "Belief in Allaah also necessitates love for His sake, hate for His sake, and making friends and enemies for His sake..."
Shaikh ‘Abdul-’Aziz ibn ‘Abdullaah ibn Baaz (rahimahullaah), in his work The Authentic Creed And The Invalidators of Islaam, said:
“Belief in Allaah also necessitates love for His sake, hate for His sake, and making friends and enemies for His sake…”
On the authority of Abu Hurrairah: The Messenger of Allaah (sallallahu 'alayhi wa sallam) said: Allaah will say on the Day of Resurrection: 'Where are those who loved one another for My Glory? Today, I will shade them in My shade on the Day when there is no shade except My Shade.' Sahih Muslim 2566
The Messenger of Allaah (sallallahu 'alayhi wa sallam) said: Allaah, The Mighty and Majestic, says: 'Those who have mutual love for the sake of My Glory will have pillars of light and will be envied by the Prophets and martyrs.' [at-Tirmidhee (2390), Ahmad (5/236-237); isnaad is 'saheeh']
Al-Walaa` wal-Baraa` (Amity and Enmity), by Shaikh Saalih al-Fawzaan (hafidhahullaah):
One’s loving and hating should be for the sake of Allaah. One’s association and disassociation should be for the sake of Allaah. This principle is one of the fundamentals of the religion, one that Allaah commands us to enjoin:
Indeed there has been an excellent example for you in Ibrahim (Abraham) and those with him, when they said to their people: “Verily, we are free from you and whatever you worship besides Allaah, we have rejected you, and there has started between us and you, hostility and hatred for ever, until you believe in Allaah Alone,” except the saying of Ibrahim (Abraham) to his father: “Verily, I will ask for forgiveness (from Allaah) for you, but I have no power to do anything for you before Allaah.” Our Lord! In You (Alone) we put our trust, and to You (Alone) we turn in repentance, and to You (Alone) is (our) final Return. Quran Surah Al-Mumtahinah, ayah 4
O you who believe! Take not My enemies and your enemies (i.e. disbelievers and polytheists, etc.) as friends, showing affection towards them, while they have disbelieved in what has come to you of the truth (i.e. Islamic Monotheism, this Qur`an, and Muhammad), and have driven out the Messenger (Muhammad) and yourselves (from your homeland) because you believe in Allaah your Lord! If you have come forth to strive in My Cause and to seek My Good Pleasure, (then take not these disbelievers and polytheists, etc., as your friends). You show friendship to them in secret, while I am All-Aware of what you conceal and what you reveal. And whosoever of you (Muslims) does that, then indeed he has gone (far) astray, (away) from the Straight Path. Quran Surah Al-Mumtahinah, ayah 1
Allaah said the believers are but brothers:
The believers are nothing else than brothers (in Islamic religion). So make reconciliation between your brothers, and fear Allaah, that you may receive mercy. Quran Surah Al-Hujurat, ayah 10
The believers are caring brethren, the right predecessors are taken as good examples for those later, ask Allaah’s forgiveness and blessings on behalf of each other:
And those who came after them say: “Our Lord! Forgive us and our brethren who have preceded us in Faith, and put not in our hearts any hatred against those who have believed. Our Lord! You are indeed full of kindness, Most Merciful. Quran Surah Al-Hashr, ayah 10
Amity and love for believers:
Verily, your Wali (Protector or Helper) is Allaah, His Messenger, and the believers, – those who perform As-Salat (Iqamat-as-Salat), and give Zakat, and they bow down (submit themselves with obedience to Allaah in prayer). And whosoever takes Allaah, His Messenger, and those who have believed, as Protectors, then the party of Allaah will be the victorious. Quran Surah Al-Ma`idah, ayat 55-56