1. Achieving success in this world and the hereafter
In Sūrah al-M’uminūn, Allah mentions that the first trait of the successful is khushūʿ in ṣalāh. Allah says, “Successful indeed are the believers, who are humble in their ṣalāh” (23:1-2).
Thus, if you want true success, firstly, you must have īmān and secondly, you should perform ṣalāh with khushūʿ.
2. Becoming sin-free like a newborn
Amr b. ʿAbasah (raḍiy Allāhu ‘anhu) narrated a long ḥadīth in which he described the virtues of wuḍū’. He reported the Prophet ﷺ saying, “And if he stands to pray and praises Allah, extols Him and glorifies Him with what He is most deserving of; and shows wholehearted devotion to Allah, he will revert to being sinfree (as pure) as he was on the day his mother gave birth to him.”
ʿAmr b. ʿAbasah (raḍiy Allāhu ‘anhu) states that he heard this from the Prophet ﷺ more than seven times (Muslim).
3. Having previous sins forgiven
ʿUthmān (raḍiy Allāhu ‘anhu) performed wuḍū’ and then said, “I saw the Messenger of Allah ﷺ perform wuḍū’ like this and he then said, ‘Whoever performs wuḍū’ like this wuḍū’ of mine, then performs two rakʿah of prayer during which he does not let his thoughts wander, Allah will forgive all of his previous sins’” (Bukhārī).
4. Earning a guarantee of Paradise
ʿUqbah b. ʿĀmir (raḍiy Allāhu ‘anhu) heard the Messenger of Allah ﷺ say, “If any Muslim performs wuḍū’, and does so properly, then stands and performs two rakʿah of prayer in which he focuses with his heart as well as his face [i.e. is not physically distracted], Paradise is guaranteed for him” (Muslim).
When ʿAbdullāh b. al-Zubayr (raḍiy Allāhu ‘anhu) stood up to pray, he was described as being ‘like a stick (i.e. motionless) with khushūʿ’. Once, during the siege of the Kaʿbah, whilst he was prostrating, a catapult struck him and tore part of his garment, but he did not even raise his head!
Related Article: The Benefits of Khushuʿ in Salah