What we believe deeply impacts the way we live.
For example, if I believe, like many, that all relatively decent people go to heaven, I’ll try to live a relatively decent life and vaguely hope it is good enough. On the other hand, if I believe that Jesus is the way, the truth and the life and that no one gets to the Father but through Him, then I’m going to do is try, out of gratitude, to connect with Jesus and trust that he has saved me, and so I have no guilt in life and no fear in death.
Now, because belief matters, asking about belief can be helpful in evangelism. Look at John 11 where Jesus, in the process of raising Lazarus from the dead, engages his sister Martha in a conversation about her belief in the resurrection.
Martha, like many, confesses a general belief in the resurrection, but then Jesus asserts in verse 25-26: “I am the resurrection and the life. The one who believes in me will live, even though they die; and whoever lives by believing in me will never die. Do you believe this?”
Notice that final question because asking it prompts Martha to profess her belief in Jesus, and the same thing can happen for others when we ask them what they believe and profess what we believe about Jesus.