How is Jesus with us unto the end of the world (Matthew 28:20)
By the Holy Spirit which is the mind, power and personal presence of the very life of God that the Father sends through His Son to us.
Or to put it another way to make sure this is clear; the Holy Spirit is the presence and power of the Father manifested through Jesus Christ, His only begotten son.
This is not a separate person of the Godhead who is being sent, it is the very life of God coming to us through His Son.
Ellen White wrote it this way…
“They were two, yet little short of being identical; two in individuality, yet ONE IN SPIRIT, and heart, and character.” — (Ellen G. White, Youth's Instructor, December 16, 1897)
“The Father gave his Spirit without measure to his Son, and we also may partake of its fulness.” — (Ellen G. White, Review and Herald, November 5, 1908)
“The Holy Spirit, which proceeds from the only begotten Son of God,” — (Ellen G. White, Review and Herald, April 5, 1906)
And so she wrote:
“We want the HOLY SPIRIT, which is JESUS CHRIST.” — (Ellen G. White, Lt66, April 10, 1894)