—1 John 3:2-3 (NASB)
The Bible doesn't tell us everything, merely everything we need to know right now. We know there is a future life with Christ after this one on earth, but most of the details have not been specifically revealed, just explained in general. What will our physical state be changed to? All the explanation we need for now is given by John: "We know that when He appears, we will be like Him, because we will see Him just as He is." Our future form will be "like Him"—what that actually is and all the specific details are for a later time. What do we do in the mean time? We make ourselves ready. In this case, we purify ourself.
Throughout the Bible we are taught that sin is a pollutant of the heart, mind, and soul. To "purify" means to be rid of sin. All of the Old Testament Law concerning purification of the Temple, priests, sacrifices, people, etc. are all meant to teach us that anything dwelling in God's presence must be pure—"pollutant free". It was important to learn that it wasn't enough to make a sacrifice to God, but to have pure and true motives and attitude.
You are not pleased with burnt offering.
The sacrifices of God are a broken spirit;
A broken and a contrite heart, O God, You will not despise."
—Psalm 51:16-17 (NASB)
We don't know all the details of what God wants us to do in the next life, but He's certainly let us know what He expects of us in this life and in preparation for the next: Purify our self. Is there even the smallest of pollutants that needs to be cleansed from your life?†††