The meaning of this couplet of A’la Hadrat رَحْمَةُ الـلّٰـهِ تَـعَـالٰی عَـلَيْـه is: Sayyiduna ‘Umar Farooq-e-A’zam رَضِىَ الـلّٰـهُ تَـعَـالٰی عَـنْـهُ is the one distinguishes between the truth and falsehood, he رَضِىَ اللهُ تَعَالٰی عَـنْهُ is the leading torch bearer of guidance and he رَضِىَ اللهُ تَعَالٰی عَـنْهُ is like a sword that works wonder in favour of Islam. May millions of salutations be upon him!
As mentioned in the book Malfuzaat Ala’ Hadrat on page 277, someone asked leader of the Ahl-e-Sunnah رَحْمَةُ اللهِ تَعَالٰی عَلَيْه about the ruling regarding seeking the company of the heretics, he رَحْمَةُ اللهِ تَعَالٰی عَلَيْه replied: It is Haraam to sit in the company of the heretics, as there is a high risk of becoming heretic. Friendship with them is a fatal poison for one’s faith.
The Beloved and Blessed Prophet صَلَّى اللهُ تَعَالٰى عَلَيْهِ وَاٰلِهٖ وَسَلَّم has said: ﴿اِيَّاكُمۡ وَ اِيَّاهُمۡ لَا يُضِلُّوۡنَكُمۡ وَلَا يَفۡتِنُوۡنَكُمۡ﴾ i.e. keep them away from you and run away from them, lest they make you go astray or throw you into Fitnah (turmoil).
(Preface; Sahih Muslim, pp. 9, Hadees 7)
And the one who relies on his Nafs (lower self), in fact relies on a big liar. ﴿اِنَّهَا اَكۡذَبُ شَيۡءٍ اِذَا حَلَفَتۡ فَكَيۡفَ اِذَا وَعَدَتۡ﴾ (i.e. if the Nafs commits something by swearing then it is the biggest liar but not when he only promises [without swearing].)