Should he focus on purifying his heart or ondoing naafil acts?

Which is more important – dealing with feelings and thoughts that Allaah dislikes, such as destructive envy, hatred, arrogance, showing off, thinking highly of one's deeds, hard-heartedness, etc., which form the evil that resides in the heart, or focusing on doing outward naafil deeds suchas prayer, fasting and other acts of worship and fulfilling vows even though those other thingsare present in the heart? Please advise us, may Allaah reward you with good.
Praise be to Allaah.
Some of the acts mentioned are obligatory,and those which are obligatory should be given precedence, as Allaah says according to the hadeeth qudsi narrated from His Messenger (peace and blessings of Allaah be upon him): "My slave doesnot draw near to Me with anything more loved by Me than the religious duties I have enjoined on him." Then He says: "And My slave continues to draw near to Me with supererogatory works so that I shall love him." Outward physical acts are not valid and acceptable unless they are accompanied by appropriate actions of theheart, because the heart islike the king and the physical faculties are like his troops. If the king is evil his troops will also beevil. Hence the Prophet (peace and blessings of Allaah be upon him) said: "In the body there is a piece of flesh: if it is soundthe whole body will be sound and if it is corrupt then the whole body will be corrupt." Similarly the (hidden) actions of the heart
inevitably affect the (visible) physical actions. So precedence must be given to that which is more obligatory, whether it is called inward or outward. Perhaps things that are called inward may be more obligatory, such as refraining from destructive envy and arrogance, for that is more essential than observing naafil fasts. Or acts that are described as outward or physical may be better, such as qiyaam al-layl (praying at night), which is better than simply giving up some thoughts that may cross one's mind such as (non-destructive) jealousy, etc. Inward and outward deeds support one another, and prayer keeps one from doing evilactions and generates fearof Allaah, and has other important effects. It (prayer) is the best of good deeds and charity. And Allaah knows best.
Shaykh al-Islam Ibn Taymiyah (may Allaah have mercy on him), Majmoo' al-Fataawa, 6/381
So there is no separation between correcting what is inward and correcting what is outward or physical.
The outward acts of worship which a person performs with his physicalfaculties – if he does themfor the sake of Allaah – will undoubtedly have an effect on his inward nature.
For example, the Prophet (peace and blessings of Allaah be upon him) said: "Shall I not tell you of something that will take away the evil of the heart? Fasting three days of each month." (Narratedby al-Nasaa'i, 2386; classed as saheeh by al-Albaani in Saheeh al-Nasaa'i, 2249). The evil of the heart refers to rancour, hatred and destructive envy.
One of the most important remedies for diseases of the heart is to study and ponder the texts which include warnings to the one who leaves these diseases to fester in his heart, such as the hadeeth in which the Prophet (peace and blessings of Allaah be upon him) said: "No one will enter Paradise who has an atom's-weight of arrogance in his heart." (Narrated by Muslim, 91).
And the hadeeth according to which Hell will say, "My share is the arrogant." (Narrated by al-Bukhaari, 4850; Muslim,2846)
And the hadeeth: "On the Day of Resurrection the arrogant will be gathered like ants in the form of men." (Narrated by al-Tirmidhi, 2492; classed as hasan by al-Albaani in Saheeh al-Tirmidhi, 2025).
And the Prophet (peace and blessings of Allaah be upon him) said: "The disease of the nations who came before you has started to spread among you: destructive envy and hatred. These are the shavers. I do not mean that they shave hair but they shave away religiouscommitment. By the One in Whose hand is my soul,you will not enter Paradise until you believe,and you will not believe until you love one another. Shall I not tell you of something which ifyou do it, you will love one another. Spread (the greeting of) salaam amongst yourselves." (Narrated by al-Tirmidhi, 2510; classed as hasan by al-Albaani in Saheeh al-Tirmidhi, 2038).
Whoever ponders with true insight such warnings about the diseases of the heart will undoubtedly strive to cleanse his heart thereof, and will seek help in doing so by doing outward physical acts, praying to his Lord to cleanse his heart of hatred, destructive envy, rancour and so on, as Allaah says, describing theprayer of the believers:
"and put not in our heartsany hatred against those who have believed"
[al-Hashr 59:10 – interpretation of the meaning]
And Allaah knows best.
Keyword: Acts of Worship