I truly believe in Christ. I love a girl who is a non-Christian. We love each other so much we want to be united. But she belongs to a rich Hindu family and I am in a lower middle class family. How do we convince her parents to approve our marrage? We want both the families to accept us . Any suggestions?
You can't make people change. You can only encourage them to change.
If you want her family to agree to your marriage, then you have to show yourself to be a man whom they can trust their daughter to. She has to show that she is happy with you and that she trusts you to take care of her. However, even with this, the Hindu view of castes will likely get in your way. Do your best, but also have plans for how you will handle their rejection if it comes to that.
I don't recommend Christians marrying non-Christians because the odds are that she will pull you away from Christ. Also you will run into problems in raising your children. They cannot be both Hindus and Christians. Often children raised in such an environment end up becoming atheists.
"But avoid foolish and ignorant disputes, knowing that they generate strife. And a servant of the Lord must not quarrel but be gentle to all, able to teach, patient, in humility correcting those who are in opposition, if God perhaps will grant them repentance, so that they may know the truth, and that they may come to their senses and escape the snare of the devil, having been taken captive by him to do his will" (II Timothy 2:23-26).