We need glorified bodies to inherit the kingdom. The kingdom is not something that Christians bring in or build. It is something that we pray to come, because we inherit it when it comes. We receive it as a gift, to which we have a right through our relationship to God as His children.
At the resurrection, when death and the grave are exposed not as victorious opponents but as defeated servants, death is swallowed up in victory!
But, as we learn from Romans 6-7, we enjoy already the resurrection victory of Jesus as we walk in newness of life. Death and sin lost their claim upon us when we died in Jesus Christ. The one that belonged to them died in Christ; the one that we are now is a slave of Christ.
This is why we must be steadfast in the work of the Lord Jesus--we are His slaves, so let us stick with His work! This is why we must be immovable in the work of the Lord Jesus--we are His slaves, so let us not depart from His work! This is why we must be abundant in the work of the Lord Jesus--we are His slaves, so let us be overflowing with His work!
Jesus frees us--not to be slaves to ourselves and our desires, but to be slaves to Him. Every time we say no to sin, no to self, and yes to Jesus, we are already now enjoying resurrection victory!