as His divine power has given to us all things that pertain to life and godliness, though the knowledge of Him who called us by glory and virtue,
by which have been given to us exceedingly great and precious promises, that through these you may be partakers of the divine nature, having escaped the corruption that is in the world through lust."
2 Peter 1:2-4 (NKJV)
Normally when you go to a store to buy something you will get a receipt. Once you have paid for the item it is yours and the receipt is the proof of purchase. It could be that what you bought was expensive, like a phone or a computer, and it was something you had wanted for a long time, so at first it is almost too good to be true that it is yours. Someone could stop you outside of the store to question you about what you bought, but no matter what they said you know the item is paid for and you have the proof of purchase to show it is yours.
In the Bible we learn about all of the things that God provided for us through Jesus. Through His death and resurrection, Jesus paid for everything we would need to live the abundant life that He came to bring. When you learn about what Jesus did it might not seem real to you, like it is too good to be true, or someone may tell you that it does not really belong to you for some reason. But, with God's Word showing us the proof of what Jesus purchased for us we can know what belongs to us, this is why it is so important for us to read and study the Bible.
If you are not sure something belongs to you, or if you do not have a proof of purchase, someone could claim that thing was theirs or convince you that what you had really belonged to someone else. When you know something belongs to you, then you will not only ignore anyone who tries to tell you otherwise, but you would even resist any attempts of someone trying to take it away from you. As we grow in our understanding of everything that Jesus provided for us we grow in faith and our confidence of what belongs to us. The Bible is our proof of purchase for everything that God provided for us through Jesus.