The answer to your question can be found by examining the entire text in which that phrase is included.
If there be therefore any consolation in Christ, if any comfort of love, if any fellowship of the Spirit, if any bowels and mercies, Fulfill ye my joy, that ye be likeminded, having the same love, being of one accord, of one mind. Let nothing be done through strife or vain glory; but in lowliness of mind let each esteem others better than themselves.Letting the mind that was in Christ be in us, is referring to an attitude. We are told to have the same attitude that Christ had. Verses three and four tell us how we can manifest Christ's attitude in our daily life. We must esteem others and put their needs ahead of ours. We do this as we show concern for others and not just ourselves.
Look not every man on his own things, but every man also on the things of others. Let this mind be in you, which was also in Christ Jesus: Who, being in the form of God, thought it not robbery to be equal with God:
But made himself of no reputation, and took upon him the form of a servant, and was made in the likeness of men: And being found in fashion as a man, he humbled himself, and be came obedient unto death, even the death of the cross. Wherefore God also hath highly exalted him, and given him a name which is above every name."
(Phil. 2:1-9 KJV)
This attitude caused Jesus to be exalted. It is the only attitude that Jesus will promote in the kingdom of God. Having the same mind as Christ is having the attitude of a servant.
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