In explanation of this verse, Imām As-Sa’di (rahimahullāh) said:
Meaning aid one another upon Al-Birr (righteousness),
It is a comprehensive phrase for everything which Allāh loves and is pleased with; from outward and inner actions; from the rights of Allāh and rights of mankind.
And Taqwa (piety) in this context(1) is a comprehensive phrase for everything which Allāh and His messenger dislikes from the outward and inner actions.
And (furthermore) every good quality is commanded to be performed, likewise every evil trait is commanded to be abandoned.(2) Indeed the servant is commanded with having good characteristics and performing the good actions himself whilst aiding others from his believing brothers upon them, with every statement and action; inducing and encouraging himself and others upon good.
Shaykh Muhammad ibn Sālih Al-Uthaymīn (rahimahullah) said:
Know that At-Taqwa is sometimes connected with Al-Birr, as is in His statement: Help you one another in Al-Birr and At-Taqwa (Al-Māidah: Verse 2). And sometimes it is mentioned by itself, so if it is connected with al-Birr, Al-Birr becomes the performance of the commandments and At-Taqwa is abandoning the prohibitions. However, if they are mentioned individually it becomes comprehensive and includes performing the commandments and avoiding the prohibitions. Verily, Allah has mentioned in His Book that paradise is prepared for the muttaqīn, therefore the people of taqwa are the people of paradise – May Allah make us and you from them – due to this it is mandatory upon the people to fear Allāh – azza wa jal – complying with His commands, seeking His reward and salvation from His punishment.(3)
Taysīr Al-Karīm Ar-Rahmān fee Tafsīr Kalām Al-Mannān Page 228 – Slightly Paraphrased
(1) Definition of Taqwa by Talq ibn Habīb (rahimahullāh)
‘’It is to act in obedience to Allah, with a light from Allah (i.e. Eemān) and hoping for Allāh’s Mercy. And that you abandon disobedience to Allāh with a light from Allāh and fearing the punishment of Allāh. [Reported by Ibn Abī Shaybah 11/33 and Ibnul Mubārak in Az-Zuhd 473]
(2) Similar was mentioned in Tafsīr At-Tabari of the same verse; Al-Birr is (to perform) that which you have been commanded with, and At-Taqwa is (to abandon) that which you have prohibited from. In Tafsīr ibn Kathīr, he (rahimahullah) says, Performance of the righteous actions is Al-Birr and abandoning the evil reprehensible acts is At-Taqwa
(3) Sharh Riyādhus Sālihin by Shaykh Muhammad ibn Sālih Al-Uthaymīn (rahimahullah), Introduction to Chapter 6 (At-Taqwa)