Al-Azhari said: ''A servant's love for Allah and His Messenger means obeying them and following their command.'' 

Al-Baydaawi said: ''Love is the will to obey.'' 

Ibn 'Arafah said: ''Love in the language of Arabs means willing a thing uprightly.'' 

Az-Zajjaaj said: ''Man's love for Allah and His Messenger is to obey them and to accept what Allah (swt) has commanded and the Messenger of Allah (saw) has brought.'' 

Allah's love for His servant means forgiveness, acceptance and reward. Al-Baydaawi said: ''He loves you and that he will forgive you means, He will be pleased with you.'' 

Al-Azhari said: ''Love of Allah, for His servant, is His blessing of his servant with forgiveness.'' He (swt) said: 

''Allah does not love the disbelievers.'' [ Aali 'Imraan: 32] i.e. He will not forgive them. Sufyan b. 'Unaynah said: ''He loves you means, He will be close to you. Love is closeness. Allah does not love the Kafireen means He will not bring the Kafireen close (to Him).'' 

Al-Baghawi said: ''Love of Allah for the believers means His commendation, reward and forgiveness for them.'' 

Az-Zajjaaj said: ''Love of Allah for His Creation means His forgiveness for them and His blessings, mercy, forgiveness and good commendation of them.'' 

However what concerns us here is the servant's love for Allah and His Messenger. This love in the above meaning is obligatory. Since love is an inclination (mayl) which shapes the behavioural disposition (nafsiyyah) of man. These inclinations can either be instinctive having no relationship to a concept, such as man's inclination towards ownership, love for survival, justice, family and children etc. They might also be motives linked to concepts, which then define the type of inclination. The American Indians did not like the immigrants who came from Europe whilst the Ansar loved those who migrated to them. The love of Allah and His Messenger is the type Allah (swt) has linked to a Sharee'ah concept thereby making it obligatory. The evidence for this is the Book of Allah: 
He (swt) said: 

''And of mankind are some who take (for worship) others besides Allah as rivals (to Allah). They love them as they love Allah. But those who believe, love Allah more (than anything else).''[ Al-Baqarah: 165] 

It means the believers' love of Allah is more than Mushriks' love to the rivals of Allah. 

''Say: If your fathers, your sons, your brothers, your wives, your kindred, the wealth that you have gained, the commerce in which you fear a decline, and the dwellings in which you have delight in are dearer to you than Allah and His Messenger, and striving hard and fighting in His Cause, then wait until Allah brings about His Decision (torment). And Allah guides not the people who are Al-Fasiqun (the rebellious, disobedient to Allah).''[ At-Tawbah: 24] 

As for the evidences from the Sunnah they are the following: 

Anas (ra) narrated: 

''That a man asked the Prophet (saw) about the final Hour. He asked: when is the final hour? He said: What have you prepared for it? He said: nothing, but I love Allah and His Messenger. He said: you will be with the one you love. Anas said: nothing made us so overjoyed more than when we heard the Prophet saying you will be with the one you love. Anas said: I love the Prophet, Abu Bakr and 'Umar and I wish to join them because of my love for them even though I have not done as many good deeds as them.''(Agreed upon). 

Anas (ra) narrated that the Prophet (saw) said: 

''There are three things whoever obtains them he will experience the sweetness of belief - that Allah and His Messenger are more beloved to him than anything else; that he loves a man only for the sake of Allah; and that he dislikes the thought of reverting to disbelief as much as he would dislike being cast into the Fire.'' (Agreed upon). 

Sahl b. Sa'd narrated that the Messenger of Allah (saw) said on the day of Khaybar: ''Qutaybah bin Said informed us, Ya'qoob bin ''abder-Rahman informed us from Aby  Haazim, he said Sahlu bin Sa'd (r.a) told me that the Messenger of Allah (saw) said on the day of Khayber: I shall give this banner to a man who loves Allah and His Messenger and they (Allah and His Messenger) love him.'' All the Muslims came forward in the following morning hoping to be granted the honour of carrying the banner. The Prophet (saw) called for 'Ali bin Abi Talib. He was told, O Messenger of Allah (saw), his eyes hurt. He said, call for him. He was brought to him, and the Messenger of Allah (saw) spat in his eyes and made du'aa' for him, so he was cured as if he had no pain before. Then he handed the banner to him. 'Ali, on his part, pledged he would fight the enemies until they embraced Islam. The Prophet (saw) answered him saying: ''Take things easy and invite them to accept Islam and brief them on their duties towards Allah. I swear by Allah that if only one person should be guided at your hands, that would surely outweigh the best of our camels.''(Agreed upon) 

Muhammad b. Sireen said: 

''People were reminiscing in the time of Umar (ra) as if they preferred Umar over Abu Bakr. When this news reached Umar b. al-Khattab (ra) he said: By Allah, a night with Abu Bakr is better than the family of 'Umar. The Prophet went out with Abu Bakr towards the Cave of Thawr, Abu Bakr sometimes would go ahead of the Prophet and sometimes behind him. The Prophet saw his uneasiness. He asked Abu Bakr, ''O Abu Bakr, What is the matter? Sometimes you are walking behind me and then sometimes you go ahead of me.'' He replied, ''O Messenger of Allah, when I think of the enemies that they might be pursuing you, I walk behind you, but when I think of some ambush I go in front of you.'' So he said: O Abu Bakr! Do you wish that something happened to you rather than to me? He said, yes, by Him Who sent you with truth, I wish no hardship but occur to me rather than to you. It is also reported that when the two arrived at the cave of Thawr, Abu Bakr requested the Prophet to wait until he had searched and cleaned up the cave. He went in and searched it and came out after cleaning it up. Then he remembered that he had not properly searched one hole. He again requested the Prophet to wait a bit and went in to see it for the second time. After he was fully satisfied that the place was safe and had no harmful insects or reptiles he said: enter O Messenger of Allah. 'Umar said: By the one in whose hands is my soul! That night was better than the family of 'Umar.'' (Reported by al-Hakim in his al-Mustadrak. He said the isnad is sound according to the condition of the two shaykhs ie. Al-Bukhari and Muslim, even though it is mursal. This mursal is of a type, which is accepted.

Anas b. Malik (ra) narrated that: 

(When the enemy got the upper hand) on the day of the Battle of Uhud, the Messenger of  Allah (saw) was left with only seven men from the Ansar and two men from the Quraysh. When the enemy advanced towards him and overwhelmed him, he said: Whoso turns them  away from us will attain Paradise or will be my Companion in Paradise. A man from the  Ansar came forward and fought (the enemy) until he was killed. The enemy advanced and overwhelmed him again and he repeated the words: Whoso turns them away, from us will  attain Paradise or will be my Companion in Paradise. A man from the Ansar came forward  and fought until he was killed. This state continued until the seven Ansar were killed (one  after the other). Now, the Messenger of Allah (may peace be upon him) said to his two  Companions: We have not done justice to our Companions. (Muslim) 

'Abdullah b. Hisham said: 

We were with the Prophet (saw) when he took the hand of 'Umar. Umar said: ''I love you more than anything except my soul which is between my two sides.'' The Prophet replied, ''None of you will believe until I am dearer to him than his own soul.'' 'Umar said, ''By the One who sent down the Book on you, I love you now more than my soul which is between my two sides.'' The Prophet said, '''Umar, now you have it!''(al-Bukhari) 

An-Nawawi reported in his commentary (Sharh) of Sahih Muslim the meaning of loving the Messenger (saw) on the authority of Sulayman al-Khattabi which states: 
''You will not be true in your love for me until you exhaust yourself in my obedience, until you prefer my pleasure over your whims even if it may lead to your death.''