These actions are the "pillars of Islam" b/c they reveal whether a person actually recognises Allah.
The disbeliever sees his wealth as his. Shuʿayb's (as) people said:
أَصَلَاتُكَ تَأْمُرُكَ أَن نَّتْرُكَ مَا يَعْبُدُ آبَاؤُنَا أَوْ أَن نَّفْعَلَ فِي أَمْوَالِنَا مَا نَشَاءُ https://twitter.com/hwmaqbul/status/1358848329694724104
The disbeliever sees his wealth as his. Shuʿayb's (as) people said:
أَصَلَاتُكَ تَأْمُرُكَ أَن نَّتْرُكَ مَا يَعْبُدُ آبَاؤُنَا أَوْ أَن نَّفْعَلَ فِي أَمْوَالِنَا مَا نَشَاءُ https://twitter.com/hwmaqbul/status/1358848329694724104
The believer sees his wealth as being from the rizq & fadl of his Creator. Shuʿayb responds back:
يَا قَوْمِ أَرَأَيْتُمْ إِن كُنتُ عَلَىٰ بَيِّنَةٍ مِّن رَّبِّي وَرَزَقَنِي مِنْهُ رِزْقًا حَسَنًا
Being a prophet, he knows who everything belongs to and who is in charge: Allah.
يَا قَوْمِ أَرَأَيْتُمْ إِن كُنتُ عَلَىٰ بَيِّنَةٍ مِّن رَّبِّي وَرَزَقَنِي مِنْهُ رِزْقًا حَسَنًا
Being a prophet, he knows who everything belongs to and who is in charge: Allah.
Since delinquency in zakat & withholding it = a corruption in living by tawhid, the negative impacts of it are serious, manifesting even on the natural plain:
"Never do people withhold alms from their wealth but that a portion from the sky will be held back..." (al-Tabarani)
"Never do people withhold alms from their wealth but that a portion from the sky will be held back..." (al-Tabarani)