There is a mutual indwelling which will occur between Jesus and the one who spiritually eats of Him. He is speaking of intimate fellowship. Note the following for McGarvey’s thoughts on the verse:

“The thought of drinking blood was startling to the Jew, for he was forbidden to taste even the blood of animals, and the reason assigned was very pertinent—because the blood was the life of the animal (Ge 9:4 Le 17:10-14). By insisting, therefore, on the drinking of his blood, Jesus has insisted that his very life to be absorbed and assimilated. To be disciples of other teachers it is only necessary that we accept and follow their doctrine. But to be a disciple of Christ is to do more than this. His divinity permits us to have a spiritual communion and fellowship with him, an abiding presence, an indwelling of his Spirit, and a veritable assimilation of life from him. Were it otherwise he could not be food for the spirit—bread of life. He had started to show to the Jews that he was to the spirit what bread was to the body. It was difficult to bring home to their carnal minds so spiritual a thought, and therefore Jesus clothed it in carnal metaphors and made it as plain as possible. Christians today, being more spiritually minded, and more used to spiritual language, are somewhat confused by the carnal dress in which Jesus clothed his thought.” (TFG 390)