I have fed you with milk - Paul here continues the metaphor, which is derived from the custom of feeding infants with the lightest food. Milk here evidently denotes the more simple and elementary doctrines of Christianity - the doctrines of the new birth, of repentance, faith, etc. The same figure occurs in Hebrews 5:11-14; and also in Classical writers. See Wetstein.
And not with meat - “Meat” here denotes the more sublime and mysterious doctrines of religion.
For hitherto - Formerly, when I came among you, and laid the foundations of the church.
Not able to bear it - You were not sufficiently advanced in Christian knowledge to comprehend the higher mysteries of the gospel.
Neither yet now ... - The reason why they were not then able he proceeds immediately to state.