Striving is a must in the Last 10 days of Ramadhan – Sheikh Saleh al-Fawzan (hafidhahullaah)
الحمد لله فضّل شهر رمضان على غيره من الشهور، وخصه بليلة القدر، التي هي خير من ألف شهر، والصلاة والسلام على نبينا محمد وآله وصحبه، أما بعد
All praise is due to Allaah, He gave preference to the month of Ramadhan over other than it from the (other) months, and may blessings and peace be upon our Prophet Muhammad, his family and his Companions. Allaah the Most High said:
‘We sent it (this Qur’aan) down on a blessed night in the month of Ramadhan. Verily, We are ever warning [mankind that Our Torment will reach those who disbelieve in Our Oneness of Lordship and in Our Oneness of worship]. Therein (that night) is decreed every matter of ordainments.’
And the Most High said:
‘Verily! We have sent it (this Qur’aan) down in the night of Al-Qadr, And what will make you know what the night of Al-Qadr (Decree) is? The night of Al-Qadr (Decree) is better than a thousand months [i.e. worshipping Allaah in that night is better than worshipping Him a thousand months.] Therein descend the angels and the Rooh [Jibreel] by Allaah’s Permission with all Decrees, Peace! (All that night, there is Peace and Goodness from Allaah to His believing slaves) until the appearance of dawn.’
And it is in the blessed month of Ramadhan, due to the saying of the Most High:
‘The month of Ramadhan in which was revealed the Qur’aan, a guidance for mankind and clear proofs for the guidance and the criterion (between Truth and falsehood).’ [al-Baqarah (2):185]
And it is sought after in the last ten from it [i.e. from the month of Ramadhan], due to the saying of the Prophet (صلى الله عليه و سلم): ((Seek (zealously) Laylatul-Qadr in the last ten (nights) of Ramadhan.)) Agreed upon. 
So ijtihaad (striving) is a must in all of the ten nights, seeking this night, for indeed the Prophet (صلى الله عليه و سلم) said: ((Whoever stands (in prayer) during Laylatul-Qadr out of Eemaan and seeking reward, then his previous sins will be forgiven.)) And He informed, the Most High, that it is better than a thousand months, and it is called Laylatul-Qadr because in it what will be in that year is decreed, due to His saying: ‘Therein (that night) is decreed every matter of ordainments.’ [Ad-Dukhaan (44):4]
And it is the Taqdeer as-Sanawee [what has been pre-decreed by Allaah for that year], and it is the specific type of Taqdeer (decree). As for the general Taqdeer, then it is what preceded the creation of the heavens and the earth by 50 thousand years, as that is authentically reported by the ahaadeeth. And it is said: it is called Laylatul-Qadr due to it’s tremendous magnitude and it’s nobility and the meaning of His saying the Most High:
‘(It) is better than a thousand months [i.e. worshipping Allaah in that night is better than worshipping Him a thousand months.]’ [al-Qadr (97):3]
Meaning: Standing in it and performing actions in it is better than performing actions in a thousand months outside of it. And seeking it is in the odd nights of the (last) ten without doubt, due to the saying of the Prophet (صلى الله عليه و سلم): ((Seek it in the Last Ten (nights) on the night when nine or seven or five nights remain out of the last ten nights of Ramadhan [i.e. 21, 23, 25, respectively].)). 
And the twenty-seventh is considered what is most correct due to the sayings of many of the Sahaabah: that indeed it is the twenty-seventh night, from them Ibn ‘Abbaas and Ubayy bin Ka’b and other than them – and the wisdom in it’s concealment [it not being known on which night it is] is so that the Muslims strive in ‘ibaadah in all of the ten nights, just as the hour of being answered from the day of Jumu’ah has been concealed so that the Muslim strives throughout the day.
And it is recommended for the Muslim to make a lot of du’aa in it, because Du’aa in it is recommended, and he supplicates with what is reported from ‘Aa’ishah (رضي الله عنها). She said: ‘O Messenger of Allaah! If I find it, with what should I supplicate?’ He said: ((Say: Allaahumma innaka ‘afuwun tuhibbul-’afwa fa’fu ‘annee.)) It was reported by Ahmad and Ibn Maajah. 
So O you Muslims! Strive in this blessed night with Salaah and Du’aa and making istighfaar and righteous actions, for verily it is an opportunity of a lifetime, and the opportunities do not remain. For verily Allaah, glorified is He, informed that it is better than a thousand months, and a thousand months is more than 80 years [83 years and 4 months], and it is a long lifespan if the human-being spent all of it in (acting in) obedience to Allaah. So one night, and it is Laylatul-Qadr, is better than it [i.e. a thousand months of worship], and this is a tremendous virtue. And this night is in Ramadhan without question and in the Last Ten (nights) from it without doubt, and if the Muslim strove in all of the nights of Ramadhan, then indeed he will coincide with Laylatul-Qadr without question and it is hoped for him the obtainment of its goodness.
So which virtue is more tremendous than this virtue for the one who Allaah grants success! So be persistent , may Allaah have mercy upon you, in seeking this night, and strive by righteous actions so that you obtain it’s reward, for verily the deprived one is the one for whom the reward has been forbidden. And whoever the season of forgiveness passes by, and he remains burdened by carrying his sins because of his negligence and his turning away, and his lack of concern then indeed he is deprived.
O you sinful one! Repent to your Lord and ask Him for forgiveness, for indeed the door of Tawbah has been opened for you, and He calls you to it and made for you a season for goodness. In it the good deeds are multiplied and in it the evil deeds are erased, so take for yourself the means of salvation.
And all praise is due to Allaah, Lord of the ‘Aalameen, and blessing and peace be upon our Prophet Muhammad, and his family and his companions.
Source: Lesson 26 – “The Virtue of Laylatul Qadr and the importance of striving for it” from “Ittihaaf Ahlil-Eemaan bi Duroos Shahri Ramadaan”, pages 63-65 of Sheikh Saalih ibn al-Fawzan al-Fawzan (hafidhahullaah)
 Recorded by al-Bukharee (2020) and Muslim (1169)
 Recorded by al-Bukharee (2021) and (2022) with a similar wording
 Recorded by at-Tirmidhi (3513), Ibn Majah (3850). Al-Hakim said (1/530) : Saheeh upon the conditions of Bukharee and Muslim and adh-Dhahabi agreed with him.
Declared Saheeh by Shaykh al-Albaanee in Saheeh al-Jaami’ (4423)