When we wash our robes, what are we doing? And where did Jesus say the kingdom of heaven lies? "Neither shall they say, Lo here! or, lo there! for behold, the kingdom of God is within you." - Luke 17:21
Interpretation: Blessed are those who purify their hearts (work on themselves), so that they may have the right to the tree of life (pure heart/mind) and they may enter the city (experience heaven) by the gates (through the heart).