2 Peter 2:1-3
Therefore, putting aside all malice and all deceit and hypocrisy and envy and all slander, [SUP]2 [/SUP]like newborn babies, long for the pure milk of the word, so that by it you may grow in respect to salvation, [SUP]3 [/SUP]if you have tasted the kindness of the Lord.
1 Corinthians 3:1-3
And I, brethren, could not speak to you as to spiritual men, but as to men of flesh, as to infants in Christ. [SUP]2[/SUP]I gave you milk to drink, not solid food; for you were not yet able to receive it. Indeed, even now you are not yet able,[SUP]3 [/SUP]for you are still fleshly. For since there is jealousy and strife among you, are you not fleshly, and are you not walking like mere men?
Solid food has to do with being Mature in the Lord.
Milk is the pure Word of God. Also means a new Born Again Christian.