Allah comes in between a person and his heart

The more I think about it, the more I get convinced about the fact that the thing which fluctuates most is our heart. Allah said, Allah comes between a person and his heart. When i read the tafsir it said, Allah can keep away believers from disbelief and Allah can keep disbelievers from belief.  But somebody would say if Allah wills He would have straighten our hearts. But what do we achieve without effort? Are we able any materialistic amenity without effort? Then how can our heart be straightened without heart? It is scary. I spend my hours how my heart leads it to. And Allah comes between a person and his heart. So if we don't straighten our hearts, all our time is wasted. But Allah planned our hearts to fluctuate and we have to deal with it. But how? First step is realization.

We learn from following that hearts get hardened

Surah Al-Baqara, Verse 74:
ثُمَّ قَسَتْ قُلُوبُكُم مِّن بَعْدِ ذَٰلِكَ فَهِيَ كَالْحِجَارَةِ أَوْ أَشَدُّ قَسْوَةً وَإِنَّ مِنَ الْحِجَارَةِ لَمَا يَتَفَجَّرُ مِنْهُ الْأَنْهَارُ وَإِنَّ مِنْهَا لَمَا يَشَّقَّقُ فَيَخْرُجُ مِنْهُ الْمَاءُ وَإِنَّ مِنْهَا لَمَا يَهْبِطُ مِنْ خَشْيَةِ اللَّهِ وَمَا اللَّهُ بِغَافِلٍ عَمَّا تَعْمَلُونَ

Then your hearts hardened after that, so that they were like rocks, rather worse in hardness; and surely there are some rocks from which streams burst forth, and surely there are some of them which split asunder so water issues out of them, and surely there are some of them which fall down for fear of Allah, and Allah is not at all heedless of what you do.

In another place Allah reminds that hearts get blind
Surah Al-Hajj, Verse 46:
أَفَلَمْ يَسِيرُوا فِي الْأَرْضِ فَتَكُونَ لَهُمْ قُلُوبٌ يَعْقِلُونَ بِهَا أَوْ آذَانٌ يَسْمَعُونَ بِهَا فَإِنَّهَا لَا تَعْمَى الْأَبْصَارُ وَلَٰكِن تَعْمَى الْقُلُوبُ الَّتِي فِي الصُّدُورِ

Have they not travelled in the land so that they should have hearts with which to understand, or ears with which to hear? For surely it is not the eyes that are blind, but blind are the hearts which are in the breasts.

I also need to know Allah put seals on whose hearts.

Allah tells us that as well that it is those who are proud, haughty, those who follow their desires and those who transgress.

Surah Ghafir, Verse 35:
الَّذِينَ يُجَادِلُونَ فِي آيَاتِ اللَّهِ بِغَيْرِ سُلْطَانٍ أَتَاهُمْ كَبُرَ مَقْتًا عِندَ اللَّهِ وَعِندَ الَّذِينَ آمَنُوا كَذَٰلِكَ يَطْبَعُ اللَّهُ عَلَىٰ كُلِّ قَلْبِ مُتَكَبِّرٍ جَبَّارٍ

Those who dispute concerning the communications of Allah without any authority that He has given them; greatly hated is it by Allah and by-those who believe. Thus does Allah set a seal over the heart of every proud, haughty one.

Surah Muhammad, Verse 16:
وَمِنْهُم مَّن يَسْتَمِعُ إِلَيْكَ حَتَّىٰ إِذَا خَرَجُوا مِنْ عِندِكَ قَالُوا لِلَّذِينَ أُوتُوا الْعِلْمَ مَاذَا قَالَ آنِفًا أُولَٰئِكَ الَّذِينَ طَبَعَ اللَّهُ عَلَىٰ قُلُوبِهِمْ وَاتَّبَعُوا أَهْوَاءَهُمْ

And there are those of them who seek to listen to you, until when they go forth from you, they say to those who have been given the knowledge: What was it that he said just now? These are they upon whose hearts Allah has set a seal and they follow their low desires.
Surah Yunus, Verse 74:
ثُمَّ بَعَثْنَا مِن بَعْدِهِ رُسُلًا إِلَىٰ قَوْمِهِمْ فَجَاءُوهُم بِالْبَيِّنَاتِ فَمَا كَانُوا لِيُؤْمِنُوا بِمَا كَذَّبُوا بِهِ مِن قَبْلُ كَذَٰلِكَ نَطْبَعُ عَلَىٰ قُلُوبِ الْمُعْتَدِينَ

Then did We raise up after him apostles to their people, so they came to them with clear arguments, but they would not believe in what they had rejected before; thus it is that We set seals upon the hearts of those who exceed the limits.



So now we need to know how to keep our hearts straight.

Allah taught us following dua.

Surah Aal-e-Imran, Verse 8:
رَبَّنَا لَا تُزِغْ قُلُوبَنَا بَعْدَ إِذْ هَدَيْتَنَا وَهَبْ لَنَا مِن لَّدُنكَ رَحْمَةً إِنَّكَ أَنتَ الْوَهَّابُ

Our Lord! make not our hearts to deviate after Thou hast guided us aright, and grant us from Thee mercy; surely Thou art the most liberal Giver.