السَّلَامُ عَلَيْكُمْ

This statement is not just a sentence that we say, it has conditions, each of which has an evidence from the Qur’an:

1. Knowledge– you have to know what laa ilaaha il-Allah actually means.
2. Certainty – you have to be certain in your belief, you can’t have any doubt about this.
3. Acceptance – you have to accept what laa ilaaha il-Allah entails, i.e., you have to accept that you must stop worshipping other than Allah, and worship Allah alone.
4. Submission – you have to submit to Allah and His laws.
5. Truthfulness – you have to be truthful in saying it, not like the munaafiqeen.
6. Sincerity – you have to say it for Allah alone, not for your parents or anyone else.
7. Love – you have to love Allah with the love that only He deserves.

Sources:

Lecture Notes:
https://www.digitalmimbar.com/AqeedahNotesTimHumble.pdf