If we see the language in its natural pace and flow which of the following sound better? May God bestow sincerity upon me! or May God make me become sincere! or May I become sincere!
Your attempts to express a fervent wish differ in their degree of formality. bestow...upon is more formal than make me.
If you're aiming for a "natural" expression, make me become sincere should be make me sincere.
May God make me sincere!
May God grant me sincerity!