Who is the King of the Kingdom that has been ushered in, and what has been put under His power?
The King of the Kingdom just ushered in is the Messiah of Israel, the Son of God, the Savior of mankind, and the Head of the Body. Everything has been put under His power. He is Head of the Body rather than King of the Church, so believers are joint heirs, not subjects.
Les explains that the Kingdom has just been ushered in, and everything has been put under the power of the King of this Kingdom. That King, he says, is the Messiah of Israel, the Son of God, the Savior of mankind, and the Head of the Body. Les has always made the point in his teaching that Christ is not the King of the Church but the Head of the Body. If believers were under a kingship, then they could never be called joint heirs, because then they would be subjects. Earlier in the context, this same Creator and Sustainer of the universe purged our sins by Himself and sat down on the right hand of the Majesty on high, fulfilling what Psalms spoke of beforehand.