"for them to become ceremonially clean." You can also state God's role. AT: "for God to consider them to be clean again" (See: [[rc://en/ta/man/translate/figs-explicit]])
"to bring him to the Lord" or "to bring him into the Lord's presence." This was a ceremony acknowledging God's claim on the firstborn children who were male.
"open the womb" is an idiom that refers to the first baby coming out of the womb. This referred to both animals and people. AT: "Every firstborn offspring who is a male" or "Every firstborn son" (See: [[rc://en/ta/man/translate/figs-idiom]])