The thief is Satan who is the inspiration for all the evil in the world.
Whereas the `I` is Jesus who offers us EternalLife and AbundantLife.

This verse is a powerful statement contrasting the nature of the enemy with the nature of our Lord Jesus Christ.

Note that the enemy takes by force what is ours, while we must appropriate by faith what is ours in Christ Jesus.
The appropriation is not a `one and done` thing. Rather, it is an ongoing process throughout our lives on this earth.

Jesus has given us His life in giving us His HolySpirit who is in every believer who has asked to be filled. We aught to invoke His life into every aspect of our walk in the earth.