Paul's three appeals concentrates on the word "same": (a) that: you all say the same thing, (b) that is, that there be no divisions among you, (c) rather, that you be knit together in the samemind and the same opinion.
Their various leaders: Paul (established the church), Apollos (taught the church), Cephas or Peter (may have visited Corinth). It is likely that the Corinthians, through their love of wisdom and a fascination for the values of the Greek philosophical, rhetorical tradition, saw Apollos as best fitting their new understanding of wisdom (Ac 18:24).
"I follow Christ": some people who form no distinct group but who attempt to rise above the rest; they too have fallen into the trap of spiritual elitism.
"Not in wisdom (Greek sophia) of word (Greek logos)": not with a kind of sophia that is characterized by rhetoric (or perhaps reason or logic). The emphasis is both on content (contrasting divine wisdom of the cross with human wisdom) and on form (in contrast to the Greek rhetorical tradition) of the gospel.
"message" (Greek logos) of the cross: the same term as "word" in v.17 but completely different
1:20 God nullified their human wisdom ("wise man"), both Greek thinkers or philosophers ("philosopher of this age") and Jewish rabbis and teachers of the law ("scholar").
Jews asked Jesus (e.g. Mt 12:38, Jn 6:30) for a "miraculous sign", i.e., asked Jesus to validate his messianic credentials with powerful displays. Greeks "look for wisdom" because they conceive God as ultimate Reason. They demand for power and wisdom, two idolatries of our fallen world.
To the Jews, the message of a crucified Messiah was the ultimate weakness (see Dt 21:23), in contrast to their demand for power. To the Gentiles, the message of a crucified Christ was utter foolishness, in contrast to their demand for wisdom.
Yet "to those whom God has called", Christ is the power and the wisdom of God.
Corinthians were not wise (wisdom), not influential (power), not well born by human standards (standards of the ‘flesh'). Sophists (Greek philosophers who emphasized wisdom) boast that they belonged to the "wise, powerful, and well born."
God aligned himself with the disenfranchised and overthrew the world's false standards of wisdom and power.
rhetorical: God chose the "nothings" to nullify the "something" (to turn the something into nothing).
"so that": the ultimate purpose; "boast": to put one's full confidence in
Corinthians are boasting (see 1:29-31, 3:21, 4:7) and being "puffed up" (see 4:6,18-19) in the name of wisdom. The reminder of their origin from the lower classes is to stop their boasting in human wisdom.
Three metaphors of our salvation: (a) righteousness: justification in the past, (b) holiness: ethical living in the present, (c) redemption: deliverance from the bondage of sin in the future.