John Gill Commentary Mark 3:14

"And he appointed twelve, that they might be with him, and that he might send them forth to preach," — Mark 3:14 (ASV)

And he ordained twelve
Or made, constituted, and appointed twelve men, out of those he called to him. The Arabic version adds, "and called them apostles"; which seems to be taken out of (Luke 6:13) .

That they should be with him ;
constantly, in private and in public; be taken into his family, and reckoned such; be his familiars, and privy to all his affairs; hear all his discourses, and see his miracles; that so they might be trained up and fitted for the great work he designed them for:

and that he might send them forth to preach ;
the Gospel in Judea first, and then in all the world: for he did not at this time send them to preach, only chose; called, and appointed them; and after they had been with him some time, and were better qualified for such service, he sent them forth, as in (Matthew 10:1Matthew 10:5) , for this constitution of them was before that mission, and was in order to it.