Paul identifies three groups in chapter 3:

1. natural man, 2:1
2. spiritual man, 3:1
3. babes in Christ, 3:1
  

“as people of the flesh”
This is “sarkinos” in Greek. The inos ending means “made of” or “derived from” (e.g., “hearts of flesh,” cf. II Cor. 3:3) so this would mean “made of flesh.” Paul uses the word “flesh” in several different ways (see Special Topic at 1:26). This context (i.e., “as to infants in Christ”) seems to use it of believers who have the Spirit, but walk after the ways of the world.

This is not Paul’s flesh vs. Spirit (cf. Rom. 8:1-11), but a category of believers. If this is true this context is one of the few places in the NT that this distinction is made. Here is the tragedy of salvation without sanctification. Claiming Christ as Savior, but not living as if Christ is Lord. If this appalling spiritual condition is characterized by jealousy, strife, and a factious spirit, what of the modern church? Oh, the tragedy of “baby Christians” to the Kingdom of God and the heart of the King!

• “as to infants in Christ” Every believer starts as a baby Christian. There is no shame in this. This is the origin of the familialmetaphor derived from the concept of being “born again” (cf. John 3:3; II Cor. 5:17; I Pet. 1:3,23), but we must not stay infants!

• 3:2 “I gave you milk to drink” This is a continuing metaphor of the new Christian as being a brand new creature characterizedas a child (cf. Heb. 5:12-14; I Pet. 2:2). Tertullian and Hippolytus tell us that the early church gave a glass of milk to the newconverts at their first communion as a symbol of this very truth.

• “for you were not yet able to receive it” By the time Paul wrote this letter, many months had passed. Although it is appropriate to be a baby Christian at the beginning of the Christian life, it is a tragedy to still be a baby Christian after many years.  (1)

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(1) Dr. Utley, Free Bible Commentary, http://freebiblecommentary.org/pdf/EN/VOL06.pdf,pp. 47-48.