1 [Prophet], have you considered the person who denies the Judgement? 2 It is he who pushes aside the orphan 3 and does not urge others to feed the needy. 4 So woe to those who pray 5but are heedless of their prayer; 6 those who are all show 7 and forbid common kindnesses.
The Long and the Short of it
Among the most amazing themes in the Quran is how structurally longer surahs are different from the shorter ones. Shorter surahs usually have a lot of meaning woven into the fabric of each ayat while longer Surahs have more rulings, stories, and explanatory material. This is from the wisdom of Allah, and was especially crucial as most of the shorter surahs in the Quran were means of da’wah to the non-Muslims of Makkah who were staunchly opposed to the Quran.
Moreover, Allah in His infinite wisdom knows that we as people, as Muslims, would usually pick the shorter surahs to memorize and recite in their prayers. Therefore, shorter surahs also contain very easy lessons in faith and worship. For example, Surah Ikhlas is a very short summary and definition of who Allah is, Surah Kawthar is a very short description of the greatness of the Prophet sallallahu alayhi wasallam, Surah Asr is a short summary of the whole message of Islam and Surah Nasr is a short summary of the promise of victory, and how to behave when Allah does give us victory. Similarly, is Surah al-Ma’un another very early Surah revealed to the Prophet sallallahu alayhi wasallam.
Denial of charity = denial of faith and day of judgement?
It is very interesting that when Allah starts with, [Prophet], have you considered the person who denies the Judgement? the first thing that could be expected in that setting would be of how the Quraysh worship idols and do not worship Allah, how they have denied the existence of Hellfire and Paradise and are intent on this life alone. Yet, the first thing that Allah mentions is that they do not give charity. It is a sign that Allah wants us to learn— that the strength of our belief in the Day of Judgement is directly proportional to the quality of charity that we give, the amount of care we have for orphans and the needy.
The Prophet sallallahu alayhi wasallam said, “as-sadaqatu burhaan” (charity is a proof).  In that same hadeeth the Prophet sallallahu alayhi wasallam also said, “The Qur’an is either an argument for you or against you” - meaning the Quran will either testify for us on the Day of Judgement or against us. It is up to us to decide which way for it to go after reading these ayaat and also the hadeeth mentioned!
The categories in which Allah mentions that we can give our charity is mentioned in one ayah in Surah Tawbah: Alms are meant only for the poor, the needy, those who administer them, those whose hearts need winning over, to free slaves and help those in debt, for God’s cause, and for travellers in need. This is ordained by God; God is all knowing and wise. 
Laziness and showing off in prayer— shortcut to Jahannam
The second characteristic that Allah shows of those who He mentions are in denial of the Day of Judgement are those those who pray 5 but are heedless of their prayer; 6 those who are all show.
This is a very serious case of riya, or showing off. In fact, this is an act of minor shirk as we are doing our worship to please the people and not to please Allah. And the punishment that Allah mentions for those who are heedless of their prayer, and are all about show, is wail, translated here as “woe.” The Prophet sallallahu alayhi wasallam mentions that wail is a valley in hellfire, which is so bad that even the hellfire itself seeks Allah’s protection from it. 
Just as charity is a proof of our belief in the Day of Judgement, so is our prayer a proof of our strength in belief in the hereafter. From the 3rd ayah of Surah Baqarah, where Allah says concerning those who have taqwa (those who are conscious about Allah), who believe in the unseen, keep up the prayer, and give out of what We have provided for them. It is interesting that Allah mentions belief in the unseen and then tags it up with keeping up the prayer and giving charity; it’s almost as if the quality of our prayers, our dedication to them, and our charity are indications of the degree of strength of our belief in the hereafter!
Knowledge of the Quran and understanding it is key in being more mindful of Allah and also in understanding the words we say in our prayers. The more we understand our prayers, the more we are likely to have better prayers, concentrate more in them, and enjoy praying to Allah. Join UnderstandQuran’s 50% of Quranic words course, which will help you understand the smaller surahs in the Quran and also all that we say in our prayers.
References: Hadeeth narrated in Saheeh Muslim  Ibid.  Quran ch-9 V-60  Hadeeth narrations in at-Tirmidhi