Imam explains the matter through his theological works as follwoing:
Abstain from everything that resembles riya’ and simulation, however virtuous it may appear to be. Even in the matter of obligatory religious duties, if you believe that you cannot perform them sincerely in public, perform them secretly, though it is preferable to perform them openly.
It is rare for riya’ to occur in obligatory duties themselves; more often it relates to their mode of performance and to acts which are mustahabb or supererogatory.
In any case, purge your heart from the dirt of polytheism with perfect solemness and severest self-criticism, lest, God forbid, you should pass away from this world in this state that your performance is deplorable, and there is no hope of salvation for you.
Then you will invite the wrath of God, as mentioned in the tradition quoted in Wasa’il al-Shi’ah from Qurb al- asnad, and reported from Amir al-mu’minin ‘Ali (A):
Amir al-mu’minin ‘Ali (A) reports that the Prophet (S) said, “One who does some act liked by God in order to show off to people, and in secret manifests such qualities as are abominations to God, he shall encounter God’s anger and wrath on the Day of Resurrection.”
There are two probable interpretations of this hadith. Firstly, it is about such a person who presents himself as paragon of virtue before people, while his inner self is immersed in ugly vices. Secondly, it may be about a person who performs outwardly virtuous deeds with the intention of Riya’.
In any case, it is obvious that the hadith condemns riya’, because the performance of the obligatory acts and duties if not motivated by riya’, cannot be the object of Divine wrath. In all probability the second meaning is closer to the import of the hadith, as the open performance of wicked deeds is a greater evil.
This is a warning for us to be cautious lest, God forbid, we do something to incur the wrath of the King of kings and the Most Merciful of the merciful.