1 Kings 3:3 Solomon showed his love for the LORD by walking according to the instructions given to him by his father David, except that he offered sacrifices and burned incense on the high places.
"High places" in Israel were places of pagan worship and are always condemned throughout the OT history. High places were locations of pagan alters and disgusting worship practices ranging in activities from simply burning incense to pagan deities, to child sacrifice. Here is a sample:
- Lev 21:28, 22:41 - high places are the locations for worshiping the false gods of Moab & Arnon
- Num 33:52 - Israel told to destroy the high places and demolish the altars there.
- 1 Kings 3:2-4 - this is possibly the exception but not really. While the temple did not exist, there was still a sanctuary where all sacrifices should have been offered (Deut 12:2, 3), but Solomon disobeyed this instruction and offered sacrifices elsewhere.
- 1 Kings 11:8 - Solomon built places of worship, high places (forbidden by Deut 12:2, 3) for his foreign wives and their false gods.
- 1 Kings 12:31, 32 - Jeroboam built shrine in many high places contrary to the instruction in Deut 12:2, 3.
- 1 Kings 13:2, 32, 33 - Jeroboam continues to defy the LORD by building high places of worship
- 1 Kings 14:23 - Asherah poles (essentially phalic symbols) we built on high places for disgusting pagan practices.
- 1 Kings 15:14 - good king Asa sinned by NOT removing the high places
- 1 Kings 22:43 - good king Jehoshaphat was reprimanded for NOT removing the high places of false worship
... and so forth. Thus "high places" of worship were condemned for one of two reasons:
They were places of pagan worship involving disgusting practices
Even when they were places where (at least notionally) the LORD was worshipped, they should not have existed because of the clear instruction in Deut 12:2-7
2 Destroy completely all the places where the nations you are dispossessing have served their gods—atop the high mountains, on the hills, and under every green tree. 3 Tear down their altars, smash their sacred pillars, burn up their Asherah poles, cut down the idols of their gods, and wipe out their names from every place. 4 You shall not worship the LORD your God in this way.
5 Instead, you must seek the place the LORD your God will choose from among all your tribes to establish as a dwelling for His Name, and there you must go. 6 To that place you are to bring your burnt offerings and sacrifices, your tithes and heave offerings, your vow offerings and freewill offerings, as well as the firstborn of your herds and flocks. 7 There, in the presence of the LORD your God, you and your households shall eat and rejoice in all you do, because the LORD your God has blessed you.