In the middle of the analogy of sheep and gates, Jesus proclaimed one of the most significant promises that are worth remembering (as well as the distinguishment from the "other guys").
First off, Jesus proclaims how the thief comes to steal, kill, and destroy (10:10). I'm pretty sure you're all familiar with the stories of the bank robber (and how those robbers are not doing good). In real life robberies, the thief not only stole objects but also ruin the lives of victims via theft. Some thieves even destroy, loot, and even kill people in the process! In a similar way, some people can "steal" our life via all sorts of bad actions, including actual theft, betrayal, and more notably, deception. Believing lies often have led people and groups -- even us -- into a bad scenario. That's no good.
But unlike the thief, Jesus comes to provide life. We've seen how Jesus guaranteed us everlasting life by believing in Him (as seen in John 3:16 and 5:24), and later on, John will talk about the crucifixion and resurrection of Jesus that demonstrates the authority of Jesus providing life. However, he doesn't just come to provide life, but to "have it more abundantly" (10:10). It's one thing to receive everlasting life (which is good), but it's another thing to have it abundantly. Jesus provides a way to experience a great, fulfilled life. Later on, Jesus talks about the significance of love, service, and Christ's counters to a messed up world with the disciples to empower them, so it's heavily implied that we receive His abundant life by walking with him like the disciples.
Speaking of life, we have the opportunity to have everlasting life (and abundant life too) because of what Jesus did, and we receive everlasting life by believing in Jesus. Believing in Jesus is essentially accepting that we need Lord Jesus (who is Son) as the one to provide everlasting life and counting on Jesus and his resurrection for giving us everlasting life as Savior. That's it for us. Jesus as Lord (and Son) powers over the lies and Jesus as Savior provides everlasting life. And not only that -- when we focus on Jesus daily and commit life in obedience, we can become disciples of Jesus and gain an abundant life.
For the readers who decided to accept Jesus and count on Him for saving us, you are guaranteed eternal life. I don't have a "I raise my hand" button or "I accepted Jesus" button because faith starts internally. (You can raise your hand though.)