What does IPC Section 153a say?

It says whoever -

1. by words, either spoken or written, or by signs or by visible representations or otherwise, promotes or attempts to promote, on grounds of religion, race, place of birth, residence, language, caste or community or any other ground whatsoever, disharmony or feelings of enmity, hatred or ill-will between different religious, racials, language or regional groups or castes or communities, or
2. commits any act which is prejudicial to the maintenance of harmony between different religious, racial, language or regional groups or castes or communities, and which disturbs or is likely to disturb the public tranquillity, or
3. organizes any exercise, movement, drill or other similar activity intending that the participants in such activity shall use or be trained to use criminal force or violence or knowing it to be likely that the participants in such activity will use or be trained to use criminal force or violence, or participates in such activity intending to use or be trained to use criminal force or violence or knowing it to be likely that the participants in such activity will use or be trained to use criminal force or violence, against any religious, racial, language or regional group or caste or community and such activity for any reason whatsoever causes or is likely to cause fear or alarm or a feeling of insecurity amongst members of such religious, racial, language or regional group or caste or community, shall be punished with imprisonment which may extend to three years, or with fine, or with both.
4. Offence committed in place of worship, etc – Whoever commits an offence specified in sub-section (1) in any place of worship or in any assembly engaged in the performance of religious worship or religious ceremonies, shall be punished with imprisonment which may extend to five years and shall also be liable to fine.