base on tafsir ibn kathir bismillah..
If someone asks, “Why does the believer ask Allah for guidance during every prayer and at other times, while he is already properly guided Has he not already acquired guidance” The answer to these questions is that if it were not a fact that the believer needs to keep asking for guidance day and night, Allah would not have directed him to invoke Him to acquire the guidance. The servant needs Allah the Exalted every hour of his life to help him remain firm on the path of guidance and to make him even more firm and persistent on it. The servant does not have the power to benefit or harm himself, except by Allah’s permission. Therefore, Allah directed the servant to invoke Him constantly, so that He provides him with His aid and with firmness and success. Indeed, the happy person is he whom Allah guides to ask of Him. This is especially the case if a person urgently needs Allah’s help day or night. Allah said,
رَبَّنَا لاَ تُزِغْ قُلُوبَنَا بَعْدَ إِذْ هَدَيْتَنَا وَهَبْ لَنَا مِن لَّدُنكَ رَحْمَةً إِنَّكَ أَنتَ الْوَهَّابُ
(Our Lord! Let not our hearts deviate (from the truth) after You have guided us, and grant us mercy from You. Truly, You are the Bestower.) (3:8). Hence,
اهْدِنَا الصِّرَاطَ الْمُسْتَقِيمَ
(Guide us to the straight way) means, “Make us firm on the path of guidance and do not allow us to deviate from it.”