All the land - See on Matthew 3:4-6 (note).

Confessing their sins - It was an invariable custom among the Jews to admit no proselyte to baptism, till he had, in the most solemn manner, declared that he forever had renounced all idolatrous worship, all heathenish superstitions, and promised an entire and unreserved submission to the law of Moses. This was necessary for a proselyte adult - a child dedicated to God by baptism must be brought up in this faith.

And there went out unto him all the land of Judea,.... The people of the land, a great number of them:

and they of Jerusalem; the inhabitants of Jerusalem, hearing of this new preacher, the new doctrine that he taught, and the new ordinance that he administered:

and were all baptized of him in the river Jordan, confessing their sins; that is, as many of them as were brought to a sight and sense of their sins, and made a confession of them, these he baptized, or immersed, in the river Jordan; for certain it is, that there were many of the Pharisees and Sadducees who came, whom he rejected; See Gill on Matthew 3:5, Matthew 3:6, Matthew 3:7.

There went out (ἐξεπορεύετο)

The imperfect tense signifies, there kept going out.

The river

Peculiar to Mark.

Confessing

See on Matthew 3:6.

And there went out unto him all the land of Judaea, and they of Jerusalem, and were all baptized of him in the river of Jordan, confessing their sins.

1:5 There went out unto him. See notes on Mt 3:5,6.

Margin sins

See Scofield Note: "Rom 3:23"

1:1-8. Isaiah and Malachi each spake concerning the beginning of the gospel of Jesus Christ, in the ministry of John. From these prophets we may observe, that Christ, in his gospel, comes among us, bringing with him a treasure of grace, and a sceptre of government. Such is the corruption of the world, that there is great opposition to his progress. When God sent his Son into the world, he took care, and when he sends him into the heart, he takes care, to prepare his way before him. John thinks himself unworthy of the meanest office about Christ. The most eminent saints have always been the most humble. They feel their need of Christ's atoning blood and sanctifying Spirit, more than others. The great promise Christ makes in his gospel to those who have repented, and have had their sins forgiven them, is, they shall be baptized with the Holy Ghost; shall be purified by his graces, and refreshed by his comforts. We use the ordinances, word, and sacraments without profit and comfort, for the most part, because we have not of that Divine light within us; and we have it not because we ask it not; for we have his word that cannot fail, that our heavenly Father will give this light, his Holy Spirit, to those that ask it.