لَعَلَّكَ بَاخِعٌ نَّفْسَكَ ...

It may be that you are going Bakhi` yourself,

means, destroy yourself -- because of your keenness that they should be guided and your grief for them.

... أَلَّا يَكُونُوا مُؤْمِنِينَ ﴿٣﴾

that they do not become believers.

Here Allah is consoling His Messenger for the lack of faith of those among the disbelievers who do not believe in him.

This is like the Ayat:

فَلاَ تَذْهَبْ نَفْسُكَ عَلَيْهِمْ حَسَرَتٍ

So destroy not yourself in sorrow for them. (35:8)

فَلَعَلَّكَ بَـخِعٌ نَّفْسَكَ عَلَى ءَاثَـرِهِمْ إِن لَّمْ يُؤْمِنُواْ بِهَـذَا الْحَدِيثِ أَسَفاً

Perhaps, you would Bakhi` yourself, over their footsteps, because they believe not in this narration. (18:6)

Mujahid, Ikrimah, Qatadah, Atiyyah, Ad-Dahhak, Al-Hasan and others said that: لَعَلَّكَ بَاخِعٌ نَّفْسَكَ (It may be that you are going Bakhi` yourself),

means, `kill yourself.'