People can do whatever they like. God gave us free will. But if people want to be saved and receive eternal life, then they must do exactly what God tells them to do, because he is the only one who is able to give such a gift/reward. That is, they must believe and be baptized (Mark 16:16).
The difference between the two approaches is summed up in two passages from Proverbs:
There is a way that seems right to a man,
but its end is the way to death.
Trust in the LORD with all your heart,
and do not lean on your own understanding.
In all your ways acknowledge him,
and he will make straight your paths.
If you want to please God and receive salvation, do what he wants, not just whatever you like.