Today's reflection [Ayah 3-5, Surah Al- Baqarah]

ٱلَّذِينَ يُؤْمِنُونَ بِٱلْغَيْبِ وَيُقِيمُونَ ٱلصَّلَوٰةَ وَمِمَّا رَزَقْنَٰهُمْ يُنفِقُونَ. (٣)

for those who believe in the existence of that which is beyond the reach of perception, who establish Prayer and spend out of what We have provided them. (2:3)

وَٱلَّذِينَ يُؤْمِنُونَ بِمَآ أُنزِلَ إِلَيْكَ وَمَآ أُنزِلَ مِن قَبْلِكَ وَبِٱلْءَاخِرَةِ هُمْ يُوقِنُونَ.(٤)

who believe in what has been revealed to you and what was revealed before you,⁷ and have firm faith in the Hereafter. (2:4)

أُو۟لَٰٓئِكَ عَلَىٰ هُدًى مِّن رَّبِّهِمْ وَأُو۟لَٰٓئِكَ هُمُ ٱلْمُفْلِحُونَ.(٥)

Such are on true guidance from their Lord; such are the truly successful. (2:5)

A lot of the things that we need to believe in , to complete our Imaan (faith) are unseen. Such as Allah himself, the hereafter, the day of reckoning, heaven or hell, angels or satan. Believing in the unseen is a prime part of faith as it helps us navigate through life whether good times or bad times. We know for sure that there is always a higher being that should be worshipped, who should be given thanks (Shukr) to during our times of blessings and bliss. As for times of trial we know we should seek his pleasure and that it is a test from Allah which will wipe our sins, raise our ranks and grant us eternal gardens of paradise if we remain patient and steadfast. Without this belief Islam is incomplete.

These ayahs also talk about establishing Salah whilst having faith in the unseen which is the core pillar of Islam. It not only grants us peace and tranquility but this special form of worship brings within us humility, guides us towards righteousness and forbids evil.
Many times Allah mentions prayer and spending in his cause together in the Quran as spending in the way of Allah is also an ibadah. Spending in His cause is not limited to just monetary or material wealth but any form of Rizq(provision). It could be talent, knowledge, physical effort, skills etc.

The belief in the hereafter holds man responsible for his actions and answerable to Allah (SWT). It also signifies that this world is a temporary place of trials and temptations. And there will be a day when each one of us will be brought to account for our actions. Only those who have established faith in the unseen and practiced the fundamental laws of divine guidance shall be the ones who truly attain success.
True success is the success of the hereafter, the achievements of the eternal world and not the achievements  of the temporary dunya which we are currently living in.