My grandparents are Hindu and very religious. They pray every day for 30 minutes and on the weekends they go to their church and stay there for hours. They are good-hearted, kind people. But can they still go to heaven if they don't follow Christianity? It's not like they don't believe in Jesus, they just don't have much knowledge because they were brought up in a different culture with a different religion.
The reason people aren't able to make it to heaven on their own is because of the problem of sin. Sin is so wide-spread, it is basically universal. "What then? Are we better than they? Not at all. For we have previously charged both Jews and Greeks that they are all under sin. As it is written: "There is none righteous, no, not one; ... for all have sinned and fall short of the glory of God" (Romans 3:9-10,23). Therefore, God came in the flesh to take care of the problem that man is unable to solve on his own. "He was in the world, and the world was made through Him, and the world did not know Him. He came to His own, and those who were His own did not receive Him. But as many as received Him, to them He gave the right to become children of God, even to those who believe in His name, who were born, not of blood nor of the will of the flesh nor of the will of man, but of God" (John 1:10-13). This new birth comes about because of Christ's death and we have access to it through baptism. "Therefore we have been buried with Him through baptism into death, so that as Christ was raised from the dead through the glory of the Father, so we too might walk in newness of life. For if we have become united with Him in the likeness of His death, certainly we shall also be in the likeness of His resurrection, knowing this, that our old self was crucified with Him, in order that our body of sin might be done away with, so that we would no longer be slaves to sin; for he who has died is freed from sin. Now if we have died with Christ, we believe that we shall also live with Him" (Romans 6:4-8).
Thus, the only way to be saved from our sins is through Jesus. "Jesus said to him, "I am the way, and the truth, and the life; no one comes to the Father but through Me"" (John 14:6). No one can reach heaven while remaining in sin, so, therefore, there is no other way to heaven but through Christ. "Enter through the narrow gate; for the gate is wide and the way is broad that leads to destruction, and there are many who enter through it. For the gate is small and the way is narrow that leads to life, and there are few who find it" (Matthew 7:13-14).
Belief in Jesus is not enough. Demons believe in Jesus and testified. "And they cried out, saying, "What business do we have with each other, Son of God? Have You come here to torment us before the time?"" (Matthew 8:29). This is why James said, "You believe that God is one. You do well; the demons also believe, and shudder. But are you willing to recognize, you foolish fellow, that faith without works is useless?" (James 2:19-20). Unless faith drives a person to obey, it serves no purpose.
Hinduism is a religion of many gods, so many that experts in the religion don't have a count. Thus, to a Hindu Jesus is just another god in a long list of gods. This is not a true belief in Jesus because the Bible describes Jesus as one of the Godhead; that is one of the three who makes up God and there is only one God. "To you it was shown that you might know that the LORD, He is God; there is no other besides Him" (Deuteronomy 4:35). To believe in Christ implies a denial of the gods of the Hindus. Their gods are unable to do anything.
"Those who fashion a graven image are all of them futile, and their precious things are of no profit; even their own witnesses fail to see or know, so that they will be put to shame. Who has fashioned a god or cast an idol to no profit? Behold, all his companions will be put to shame, for the craftsmen themselves are mere men. Let them all assemble themselves, let them stand up, let them tremble, let them together be put to shame. The man shapes iron into a cutting tool and does his work over the coals, fashioning it with hammers and working it with his strong arm. He also gets hungry and his strength fails; he drinks no water and becomes weary. Another shapes wood, he extends a measuring line; he outlines it with red chalk. He works it with planes and outlines it with a compass, and makes it like the form of a man, like the beauty of man, so that it may sit in a house. Surely he cuts cedars for himself, and takes a cypress or an oak and raises it for himself among the trees of the forest. He plants a fir, and the rain makes it grow. Then it becomes something for a man to burn, so he takes one of them and warms himself; he also makes a fire to bake bread. He also makes a god and worships it; he makes it a graven image and falls down before it. Half of it he burns in the fire; over this half he eats meat as he roasts a roast and is satisfied. He also warms himself and says, "Aha! I am warm, I have seen the fire." But the rest of it he makes into a god, his graven image. He falls down before it and worships; he also prays to it and says, "Deliver me, for you are my god." They do not know, nor do they understand, for He has smeared over their eyes so that they cannot see and their hearts so that they cannot comprehend. No one recalls, nor is there knowledge or understanding to say, "I have burned half of it in the fire and also have baked bread over its coals. I roast meat and eat it. Then I make the rest of it into an abomination, I fall down before a block of wood!" He feeds on ashes; a deceived heart has turned him aside. And he cannot deliver himself, nor say, "Is there not a lie in my right hand?" (Isaiah 44:9-20).
Hinduism is unable to solve the problem of sin and, thus, cannot lead its followers to heaven. The reason Christians teach others is because we understand that to be saved people need Jesus. "For we must all appear before the judgment seat of Christ, so that each one may be recompensed for his deeds in the body, according to what he has done, whether good or bad. Therefore, knowing the fear of the Lord, we persuade men" (II Corinthians 5:10-11).