Because Ephraim has multiplied altars for sinning, They became for him altars for sinning.
      (1.) They multiplied their altars (Hosea 8:11; Hosea 8:11): Ephraim made many altars to sin. God appointed that there should be but one altar for sacrifice (Deuteronomy 12:3; Deuteronomy 12:5); but the ten tribes, having forsaken that, would still be thought very devout, and zealous for the honour of God, and, as if they would make amends for the affront they put on God's altar, they made many altars, dedicated to the God of Israel, whom hereby they intended, or at least pretended, to give glory to; but that would not justify their violation of God's express command, nor would the example of the patriarchs, who before the law of Moses had many altars. No, they made many altars to sin (that is, they did that which turned into sin to them), and therefore these altars shall be unto them to sin, that is, God will charge it upon them as a heinous sin, and put that upon the score of their crimes which they designed to be for the expiation of their crimes. Or they shall be to them an occasion of further sin. Their multiplying of altars dedicated to the God of Israel would introduce altars dedicated to other gods. Note, It is a great sin to corrupt the worship of God, and it will be charged as sin upon those that do it, how plausible soever their pretensions may be. And the way of this, as other sins, is down-hill; those that once deviate from the fixed rule of God's commands will wander endlessly.