The only way to prove that you believe is to live consistent with that belief.
If you think you can simply declare your belief and then cruise, you might want to explore the following:
Matt 7:21 - not everyone saying “Lord, Lord” will inherit the kingdom of heaven
Matt 24:13 - those who persevere to the end will be saved
Romans 11:22 - remain in his kindness or you will be cut off
Phil 2:12 - work out your salvation in fear and trembling
1 Cor 9:27 - drive your body for fear of being disqualified
1 Cor 10:11-12 - those thinking they are secure may fall
Gal 5:4 - separated from Christ, you’ve fallen from grace
2 Tim 2:11-13 - must hold out to the end to reign with Christ
Hb 6:4-6 - describes sharers in Holy spirit who then fall away
Heb10:26-27 - if you sin after receiving the truth, judgement remains
Well now.We are saved or we are not? Which is it?? I go with “saved”. I know the Bible is littered with irreconcilable contradictions (that is why I don’t worship the Bible and consider it secretarial). but I go with John 3:16.