Thomas Aquinas, Compendium of Theology

Christ's death was like our death as regards the essence of death, which consists in the separation of the soul from the body. But in another respect the death of Christ was different from ours. We die for the reason that we are subject to death by a necessary law of nature, or in consequence of some violence done to us. But Christ did not die because of any necessity. He gave up His life by His power and His own will, as He Himself attested: "I have power to lay it [My life] down, and I have power to take it up again" (John 10:18).

The reason for this difference is that physical things are not subject to our will. But the joining of the soul to the body is physical. Hence the fact that the soul remains united to the body or that it is separated from the body, is not subject to our will, but must be brought about by the power of some agent. But whatever was physical in Christ as regards His human nature, was completely subject to His will, because of the power of His divinity, to which all nature is subject. Therefore Christ had it in His power that so long as He willed, His soul would remain united to His body, and that the instant He willed, the soul would depart from the body. The centurion standing near the cross of Christ felt the presence of this divine power when he saw Him expire with a loud cry. By this Christ clearly showed that He was not dying like other men, from the breaking down of nature. For men cannot send forth their last breath with a loud cry; in the moment of death they can scarcely move their tongue in a quavering whisper. Hence the fact that Christ died uttering a loud cry gave evidence of the divine power in Him. It was for this reason that the centurion said: "Indeed, this was the Son of God" (Matt. 27:54).

Yet we may not aver that the Jews did not kill Christ, or that Christ took His own life. For the one who brings the cause of death to bear on a person is said to kill him. But death does not ensue unless the cause of death prevails over nature, which conserves life. Christ had it in His power either to submit His nature to the destructive cause or to resist that influence, just as He willed. Thus Christ died voluntarily, and yet the Jews killed Him.