Speaking of the Kingdom, the Savior undoubtedly means the Kingdom that He Himself brought into the world, not the one that the people listening to Him usually imagined. As a rule, His listeners imagined a strong earthly state, living according to the laws of the Torah and therefore enjoying God's protection, headed by a righteous King to whom God had given special authority over the world and over people.
Such a kingdom could of course also be open not only to Jews, but all others in any case would have to become Yahwists and accept Judaism in order to make use of what the Messiah would bring into the world. Jesus, however, speaks of something else: of the Kingdom as a spiritual reality that exists independently of any earthly structures and institutions, state or social. This Kingdom enters the world through Him, and the path into it is opened by relationships with Him and with His heavenly Father. The true Kingdom of Christ is a space of relationships, and first of all the relationships that bind Christ with the Father.
And into the space of their relationship anyone can enter, regardless of language, nationality, cultural or religious tradition. Christianity is not a religion and not even a spiritual practice, but life in the Kingdom, and therefore in the space of relationship between Father and Son. Here the question of who is first and who is last is not simple. In essence, here it has no meaning at all: in the Kingdom everyone receives the fullness of life that he is able to contain. But who will partake of this fullness earlier is indeed an open question.
It would seem that in Judea in gospel times there were many people whose main goal and meaning of life was precisely the expectation of the Messiah and the Kingdom. But their expectation became for them a kind of religion, or more exactly, part of their religious life, based naturally on Judaism. And religion tends to become something valuable and self-sufficient in itself, often obscuring the goal for which it arose and exists.
On the other hand, in the world there were many people seeking, often without realizing it, precisely the Kingdom and its life, often not knowing where and from Whom to seek it. And if it was often very hard for religious messianists to reconcile themselves to the Messiah as He is, then for seekers of the Kingdom not burdened by any religion, coming to Him was much simpler and more natural. This is not surprising: Jesus Himself says that it is hard for a rich person to enter the Kingdom. And here it no longer matters whether the wealth is material, cultural, or religious.