This can be a very challenging passage to interpret. It contains a number of rather unique images and metaphors, uses words and concepts that are rare or unique in the New Testament.
The text will argue two related points, one positive and one negative. Positively, he wants to let his audience know that they are already fully experiencing a relationship with God. From the negative side he says things like “don’t let anyone judge you,” 2:16; “don’t let any disqualify you,” 2:18). Teachers are imaged as those who take people captive as prisoners. Their teachings are classified as empty and deceitful philosophy.