"Entangled" means to hold in, to ensnare. It shows legalism holds us in its grip. Legalism is a system of bondage. It will load us down with a burden. It will press us down so that we cannot live the Christian life as we should.
Note the word "again." Legalism enslaved the Judaizers in their false understanding of the Mosaic law. Also, the Galatians experienced legalism in their slavery to paganism (4:8). God liberated them from slavery to false gods but now these Galatian Christians were about to enter Judaic legalism.
And this (ho, relative pronoun—“water” is the understood antecedent) water symbolizes baptism (baptisma). Baptism represents a complete break with one’s past life. As the Flood wiped away the old sinful world, so baptism pictures one’s break from his old sinful life and his entrance into new life in Christ. Peter now applied to his readers the principle he set forth in verses 13–17 and illustrated in verses 18–20. He exhorted them to have the courage to commit themselves to a course of action by taking a public stand for Christ through baptism. The act of public baptism would “save” them from the temptation to sacrifice their good consciences in order to avoid persecution. For a first-century Christian, baptism meant he was following through on his commitment to Christ, regardless of the consequences.