The love of Allah should occupy man's heart and get total possession of it; and if it does not seize it entirely, it should at least outweigh the love of all other things in it. Allah Says about the believers, (what means): "He loves them and they love Him," [Quran 5:54] and the Prophet said: "A man would not have attained faith until and unless he loves Allah and His Messenger more than anything else."(Al-Bukhari) When angel of death came to take the soul of Prophet Ibraaheem, may Allah exalt his mention, the latter said, "Have you ever seen a friend take his friend's life?" To that, Allah replied, "Have you ever seen a friend unwilling to see his friend?" Then Ibraaheem, may Allah exalt his mention said, "O Angel of death! Take my soul!" The Prophet taught the following supplication to his Companions, "O Allah, allow me to love You and to love those who love You, and to love whatsoever brings me nearer to Your love, and make Your love more precious to me than cold water to the thirsty." (At-Tirmithi)
Al-Hassan Al-Basri used to say, "He who knows Allah, loves Him."
Causes of the love of Allah
The first cause is man's love for himself and his drive to perfect his own creation. This leads directly to loving Allah because man's very existence and attributes are but the gift of Allah whose grace and kindness have brought man from behind the curtain of non-existence into this visible world. Man's preservation and eventual attainment of perfection are also entirely dependent upon Allah's grace. It would indeed be a wonder if one should take refuge from the heat of the Sun under the shadow of a tree and not be grateful to the tree, without which there would be no shadow at all. On precisely the same way, were it not for Allah, man would have neither existence nor attributes at all.
The second cause of this love is that man loves his benefactor, and in truth, his only Benefactor is Allah, for whatever kindness man receives from fellow-creatures is due to the immediate instigation of Allah. Whatever the motive that may have prompted the kindness he receives from others, Allah is the One who set that motive to work.
The third cause of man's love of Allah is his contemplation of the beautiful Attributes of Allah, His Power and Wisdom, of which human power and wisdom are but the feeblest reflections.
Signs of the love of Allah
Many claim to love Allah. But each should examine himself as to the genuineness of the love which he professes.
The first test of how genuine the love is this: he should not dislike the thought of death, for no friend shrinks away from going to see a dear and beloved friend. The Companion Abu Moosa Al-Asha'ri, may Allah be pleased with him, narrated that the Prophet Muhammad said,"Whoever wishes to meet Allah, Allah wishes to meet him." (Al-Bukhari)
It is true, one who sincerely loves Allah may shrink away from the thought of dying before he is fully prepared to meet his beloved One in the Next World, but one would think, he should work diligently to prepare for that sure meeting ahead of time.
The second test is that one should be willing to sacrifice his own will to Allah's; should cling to what brings him nearer to Him; and should shun all that distances him from Allah. One's commission of sins is no proof that one does not love Allah at all, but it proves that he does not love Him with his whole heart. Al-Fudhayl Ibn ‘Iyaadh once said, "If any one asks you whether you love Allah, keep silent; for if you say, `I do not love Him,' you are a nonbeliever; and if you say, ‘I do' your deeds may contradict your claim.”
The third test is that the remembrance of Allah should always remain fresh in one's heart, for what one loves, one constantly remembers; and if that love is perfect, one would never forget it.
The fourth test is that he will love the Quran, which is the Word of Allah, revealed to Muhammad who is the Prophet of Allah; in fact, if his love is really strong, it will encompass the whole creation, for he who loves any one, loves the works he composes.
The fifth test is that he covets retirement and privacy for the purpose of worship and devotion; he longs for the approach of night so that he may hold association with his Friend without hindrance. If he prefers conversation by day and sleep at night to such retirement, then, his love is imperfect.
The sixth test is that worship becomes easy. A righteous man once said, "Over a span of thirty years, I performed my night-devotions with great difficulty, but during the course of the next thirty years they became a delight." When love to Allah is complete, no joy is equal to the joy of worship.
The seventh test is that one loves those who obey Allah and detest those who disbelieve in Him and disobey Him. Allah the Almighty Says (what means): "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 is the successful." [Quran 18:22] -islamweb.net