“Now the Lord Yahweh has sent me.” The subject abruptly shifts here, which is not uncommon, and Cyrus answers God’s call. Isaiah himself had answered God’s call earlier (Isa. 6:8), and now Cyrus does. God sent Cyrus and Cyrus both obeyed the call and acknowledged the God of Israel (Ezra 1:2).
“and also sent His spirit.” It was well known that for prophets and kings to be successful they had to be empowered by God’s spirit, His gift of holy spirit. That was why God put his spirit upon the elders that were to rule Israel (Num. 11:17-29), why after David sinned he prayed that God would not take His holy spirit away (Ps. 51:11), and why Elisha asked for a double portion of God’s spirit to be upon him (2 Kings 2:9), and indeed, the Bible records that Elisha did almost twice as many miracles as Elijah. Cyrus, in typical fashion of one who does not take credit not due him, acknowledges here in Isaiah 48:16 that God sent him, but will not take full credit for his success but says that God also gave His spirit to Cyrus, which was the source of much of his success. [For more on the difference between Holy Spirit, a name for God, and “holy spirit” (often just called “the spirit”) the gift of God, see Appendix 11, “What is the Holy Spirit”].