In The Name of Allaah, The Most Merciful, The Bestower of Mercy.

Allaah [The Exalted] said:

يَا أَيُّهَا النَّاسُ إِنَّ وَعْدَ اللَّهِ حَقٌّ ۖ فَلَا تَغُرَّنَّكُمُ الْحَيَاةُ الدُّنْيَا ۖ وَلَا يَغُرَّنَّكُم بِاللَّهِ الْغَرُورُ
إِنَّ الشَّيْطَانَ لَكُمْ عَدُوٌّ فَاتَّخِذُوهُ عَدُوًّا ۚ إِنَّمَا يَدْعُو حِزْبَهُ لِيَكُونُوا مِنْ أَصْحَابِ السَّعِيرِ

O mankind! Verily, the Promise of Allah is true. So let not this present life deceive you, and let not the chief deceiver (Satan) deceive you about Allah. Surely, Shaitan (Satan) is an enemy to you, so take (treat) him as an enemy. He only invites his Hizb (followers) that they may become the dwellers of the blazing Fire. [Surah Al-Faatir. Aayaat 5-6]

[يَا أَيُّهَا النَّاسُ إِنَّ وَعْدَ اللَّهِ حَقٌّ-O mankind! Verily, the Promise of Allah is true]-Meaning, Allaah’s promise regarding the resurrection and recompense for one’s deeds is true. There is no doubt, uncertainty and confusion about it because it has been established by the divine and intellectual proofs. Therefore, when it is the case that this is true, then prepare for it, hasten by utilising your precious time to perform righteous deeds and do not be hindered from it by any hindrance.

[فَلَا تَغُرَّنَّكُمُ الْحَيَاةُ الدُّنْيَا- So let not this present life deceive you] – Meaning, its enjoyment, desires and the pursuits of one’s soul (heart), and thus you are diverted from the purpose behind which you were created. [وَلَا يَغُرَّنَّكُم بِاللَّهِ الْغَرُورُ – And let not the chief deceiver deceive you about Allah] -Meaning, shaytaan is an enemy of yours in reality, so [فَاتَّخِذُوهُ عَدُوًّا ۚ- so take (treat) him as an enemy]- Meaning, take him as an enemy every time and do not be negligent in waging war against him every time, because indeed he sees you whilst you cannot see him and he is always watching you. [ إِنَّمَا يَدْعُو حِزْبَهُ لِيَكُونُوا مِنْ أَصْحَابِ السَّعِيرِ- He only invites his Hizb (followers) that they may become the dwellers of the blazing Fire]- Meaning, this is his goal and intent. so that the one who follows him is severely humiliated through severe punishment. (1)

Allaah [The Most High] said: [وَٱعۡتَصِمُواْ بِٱللَّهِ هُوَ مَوۡلَٮٰكُمۡ‌ۖ فَنِعۡمَ ٱلۡمَوۡلَىٰ وَنِعۡمَ ٱلنَّصِيرُ -And hold fast to Allah; He is your Maula (Patron, Lord, etc.), what an Excellent Maula (Patron, Lord, etc.) and what an Excellent Helper!]’ [Surah Al-Hajj. Aayah 78]

Imaam Ibnul Qayyim [may Allaah have mercy upon him] said: “When you hold fast to Allaah, He will protect you. Allaah will help you against shaytaan and (the evil urges) of your souls – the two enemies that never isolate themselves from a person. Their enmity is more harmful than an apparent enemy. Therefore, being given help against them is the most important thing and a person’s need of this help is more than (his need for other things). And the completeness of this help is (granted) based on the level of one’s attachment to Allaah”. (2)

Abu Sa’eed Al-Khudri [may Allah be pleased with him] narrated that Allaah’s Messenger [peace and blessings of Allaah be upon him] said, “Indeed shaytaan said, ‘By Your Might O my Lord! I will not cease to misguide your slaves as long as their souls are in their bodies’. The Lord (Allaah) said, ‘By My Might and Majesty! I will not cease forgiving them as long as they keep seeking My Forgiveness'”. [As-Saheehah 104]

[Ref 1: An Excerpt from Tafseer As-Sadi. Slightly paraphrased]
[Ref 2: Jalaa Al-Af’haam. Page 154]