The verses you've quoted from the Bible refer to the concept of the "kingdom of God" or "kingdom of heaven," which is a central theme in the teachings of Jesus in the New Testament. The kingdom of God is often described as a spiritual realm that is present among us but not fully realized on Earth. It is said to be characterized by righteousness, peace, and joy. The verses you've quoted refer to angels playing a role in the establishment and maintenance of the kingdom of God on Earth, and to the ultimate triumph of the kingdom of God over all other earthly kingdoms. The phrase "Thy kingdom come. Thy will be done in earth, as it is in heaven" from the Lord's prayer reflects the belief that the kingdom of God is not fully present on Earth yet, but will be fully established in the future, and the phrase "The time is fulfilled, and the kingdom of God is at hand" from Mark 1:15 reflects the belief that the kingdom of God is already here in a certain sense and that it is accessible to those who repent and believe in Jesus.

"20And when he was demanded of the Pharisees, when the kingdom of God should come, he answered them and said, The kingdom of God cometh not with observation: 21Neither shall they say, Lo here! or, lo there! for, behold, the kingdom of God is within you."

Luke 17:20-21 (KJV)
This verse is also highlighting the idea that the kingdom of God is not an external, observable physical kingdom, but rather it is within us and can be entered into by those who repent and believe in Jesus. It also emphasizes that the kingdom of God is already present on earth.