And He (Jesus) ordained twelve, that they should be WITH Him, and that He might send them forth to preach...—Mark 3:14
Preposition - A function word that combines with a noun or pronoun or noun phrase to form a prepositional phrase...A word governing a noun or pronoun expressing a relationship to another word.
The word WITH is a preposition. It's a word that shows how we are to be in relationship to Him (Jesus). It combines with the pronoun Him (referring to Jesus) and governs it by showing that we're to be WITH Him. In other words, Jesus came so that we might BE WITH HIM. His primary purpose was not that we would be FOR Him but that we should be WITH Him...
Dear friends, use your most holy faith to grow. Pray with the Holy Spirit’s help. Remain in God’s love as you look for the mercy of our Lord Jesus Christ to give you eternal life. Show mercy to those who have doubts. Save others by snatching them from the fire of hell. Show mercy to others, even though you are afraid that you might be stained by their sinful lives.