Galatians 3:23-4:7

We were held captive under the law before faith, but now that faith has come, we are all unified in Christ. We're not really separated by our ethnicity, but unified by all being found in Christ.

An analogy is used, talking about an heir growing up as a child eventually to receive his inheritance, though under guardians until the set date. Similarly, though not receiving the inheritance yet, we were held under the slavery by things of this world until we could be redeemed by Christ. Being under the law at first, we could be adopted as sons and daughters into God's family.