Summary: Water baptism is an outward sign of inward pride. Why? Because the way to be saved from hell is by faith in Jesus: by believing in his person, and in his blood as the full payment for all your sins. You will then have been sealed with that holy Spirit of promise. But many Christians don't believe in Jesus his person. Instead, they trust in the application of water to their person.
What is the objective of water baptism?
In general, the objective of water baptism is:
Together they form a descending order. Using water baptism for the first two will lead to your damnation. So, I'll focus on those.
But whatever the objective, the motivation to trust in water baptism is the same. The motivation is pride. I'll explain.
How to achieve the objective?
There is one way to be saved from hell. Singular. Salvation from hell is by grace through faith alone. Now "faith" is the substance of things hoped for. You must trust in Jesus: by believing in his person and in his blood. Why? Because God has faith in the blood of Jesus as the full payment for all your sins. If you believe that too, that is why you then believe in him. After having this faith alone, you will then have been sealed with that holy Spirit of promise.
Source: King James bible, Romans 3:24-26 (what to believe in); Ephesians 1:12-13 (when you are sealed) (Read it).
Faith in Jesus and his blood.