In each sentence, the highlighted verbal noun answers why the action occurred.
جِئْتُ طَلَبًا لِلْعِلْمِ — I came seeking knowledge.
طَلَبًا gives the reason for coming.
وَقَفَ الطَّالِبُ احْتِرَامًا لِلْمُعَلِّمِ — the student stood out of respect for the teacher.
احْتِرَامًا gives the reason for standing.
سَاعَدْتُ الْفَقِيرَ رَحْمَةً بِهِ — I helped the poor man out of compassion for him.
رَحْمَةً gives the reason for helping.