The "old" nature we are all born with has to die daily with Jesus on the cross. Then our new nature or "born again" nature is able to rejoice in Him... I can now experience rest and refreshment to my soul because of what He has done for me at the cross.
"Truly I say to you, unless you repent (change, turn about) and become like little children [trusting, lowly, loving, forgiving], you can never enter the kingdom of heaven [at all]." Matt. 18:3 "Repent (change your mind for the better, heartily amend your ways, with abhorrence of your past sins), for the kingdom of heaven is at hand.