“But I have a baptism to be baptized with, and how distressed I am till it is accomplished.”
Jesus was not speaking of a water baptism because He had already been baptized with water and not a baptism of the Spirit because as part of the Trinity, the Spirit was part of Him. What He was speaking of was the baptism of His sufferings and tortures on the cross, which could be compared to a baptism because of the abundance of them. He was immersed into them and was covered with them and when He died and was resurrected, death no longer had dominion over Him. His baptism of suffering was the will of the Father and Jesus obediently went through it. It was the reason He was born as a man for our sins could not be atoned for without the sufferings of Christ. How distressed He was until it was accomplished, Christ’s words expressed His apprehension (as man) of His sufferings, though to fulfill the law and the prophecies He knew the sufferings were necessary.