الم ﴿۱﴾ اللَّهُ لَا إِلَهَ إِلَّا هُوَ الْحَيُّ الْقَيُّومُ ﴿۲﴾ نَزَّلَ عَلَيْكَ الْكِتَابَ بِالْحَقِّ مُصَدِّقًا لِمَا بَيْنَ يَدَيْهِ وَأَنْزَلَ التَّوْرَاةَ وَالْإِنْجِيلَ ﴿۳﴾

﴾1﴿ Alif-Laam-Meeem
﴾2﴿ Allaahu laaa ilaaha illaa Huwal Haiyul Qaiyoom
﴾3﴿ Nazzala 'alaikal Kitaaba bilhaqqi musaddiqal limaa baina yadaihi wa anzalat Tawraata wal Injeel

﴾1﴿ Alif-Laam-Meeem
﴾2﴿ Allah Almighty—there is no one worthy of worship except Him. He is Ever-Living and the Sustainer of all existence.
﴾3﴿ We have sent down to you the Book in truth, confirming the Scriptures that came before it, and He sent down the Torah and the Gospel.

Relevancy:
This surah is connected to the previous one: 1. In Surah al-Baqarah, the arguments were presented in support of the Oneness of Allah (tawheed); in this surah, responses are given to objections.
2. That surah covered four topics in one manner — tawheed (Oneness of Allah), prophethood, jihad, and charitable spending; this surah addresses these topics in a different way.
3. In that surah, the refutation was primarily against the polytheism of the Jews; in this surah, the refutation is against the polytheism of the Christians.
Claim of this surah: This is an affirmation of the Oneness of Allah, along with responses to doubts. The conclusion is that you should not doubt the Oneness of Allah and the prophethood of this Messenger; rather, have certainty in them. Take part in jihad and do not be miserly. There are four main themes: tawheed (Oneness of Allah), prophethood, jihad, and spending in the path of Allah.
Summary of the surah: This surah consists of four sections. The first section, up to verse 63, deals with the Oneness of Allah (tawheed). It contains three parts: The first part, up to verse 17, includes the affirmation of tawheed along with rational and transmitted proofs, revelation, the resulting conclusion, a response to a question, the teaching of a supplication, encouragement toward piety, a mention of the lowliness of the worldly life, followed by glad tidings for those who respond (to the truth) and a description of their qualities. (Note): Approximately the first 80 verses of this surah were revealed in refutation of the Christians of Najran.

[2] In this verse, the claim of tawheed is made — that exclusive worship is deserved only by Allah Almighty. Jesus and Mary (peace be upon them) cannot be taken as deities. Worship implies dependence, for a servant is always in need, and the One who fulfills all needs is only Allah Almighty. This verse presents the claim of tawheed along with two rational proofs by mentioning the attributes of Allah.
[3] In this verse, there is a proof from revelation and a transmitted proof from previous scriptures — namely the Torah and the Gospel.