The important thing is not baptism, but sharing the good news about Jesus. Baptism shows how people respond to the message.
not with words of wisdom: This refers to speaking well or appealing to human wisdom.
lest the cross be emptied of its power: Focusing too much on eloquence and human reasoning can distract from the simple message that Christ died for people's sins so they could be forgiven (1 Corinthians 2:1–5; 15:1–3).