Abide in Me, and I in you. As the branch cannot bear fruit of itself, except it abide in the vine; no more can ye, except ye abide in Me. – John 15:4

In the New Testament the Lord Jesus explains this phrase of being in Himself: He represents us as being in Him as the branch is in the vine. Now, the branch derives all its nourishment, its sap, its vitality, its fruit-bearing power, from the stem with which it is united. It would be of no use that the branch should be placed close to the trunk, it would be of no service even to strap it side by side with the stem, it must be actually in it by a vital union. There must be sap-streams flowing at the proper season into it, life-floods gushing into it from the parent stem; and even so there is a mysterious union between Christ and His people, not to be explained but to be enjoyed, not to be defined but to be experienced, in which the very life of Christ flows into us, and we by the virtue that cometh out of Him into us, become like unto Him, and bring forth clusters of good fruit unto His honour and unto God’s glory. I trust you know what this means, beloved, many of you. May you live in the possession of it daily! May you be one with Jesus, knit to Him, united to Him never to be separated for ever. As the limb is in the body, even so may you constantly be one with Jesus. ~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/0881.cfm