in other words pick n choose what applies .
It is not arbitrary it is based on who is being addresses and what scripture says
[1Co 9:17 KJV] 17 For if I do this thing willingly, I have a reward: but if against my will, a dispensation [of the gospel] is committed unto me.
[Eph 1:10 KJV] 10 That in the dispensation of the fulness of times he might gather together in one all things in Christ, both which are in heaven, and which are on earth; [even] in him:
[Eph 3:2 KJV] 2 If ye have heard of the dispensation of the grace of God which is given me to you-ward:
[Col 1:25 KJV] 25 Whereof I am made a minister, according to the dispensation of God which is given to me for you, to fulfil the word of God;
Dispensations are Biblical