Boyd’s Bible Dictionary:
Altars, temples, and dedicated places originally on high ground
(Gen. 12:8; Judg. 6:25; Isa. 65:7; Jer. 3:6). When the groves and mounts of idolatry overshadowed true worship, “high places” became a reproach.
Concise Bible Dictionary:
The word commonly used for the high place is bamah, signifying what is high or elevated (compare Ezek. 20:29), and then the hills on which altars were erected. There were such places in Canaan before the Israelites entered it, which they were told to destroy (Num. 33:52). If the Israelites had such, God would destroy them and cut down their images (Lev. 26:30).
In the above passages the high places are connected with idolatry; but it would appear that before the temple was built, altars for the worship of God had been erected elsewhere than at the tabernacle. With Samuel at Zuph, there was “a sacrifice of the people” in the “high place” (God having forsaken the tabernacle at Shiloh, this disorder resulted). It was evidently on elevated ground, for they went up to it and came down (1 Sam. 9:12-25). At the beginning of the reign of Solomon the people sacrificed in high places because the temple was not yet built. This was failure, for we read that “Solomon loved the Lord, walking in the statutes of David his father: only he sacrificed and burnt incense in high places” (1 Kings 3:2-4). The tabernacle was there at Gibeon (1 Chron. 16:39; 2 Chron. 1:3), so that it appeared to be the right place to go to, and it was where God appeared to Solomon in the night; yet it was “the great high place.” The reason of this implied disapproval is doubtless because the ark was not there, the symbol of God’s presence, which was the true place of worship. At the close of Solomon’s life he sinned greatly in building a high place for the gods of all his strange wives (1 Kings 11:7-8). On the division of the kingdom, Jeroboam set up his idols and “ordained him priests for the high places, and for the devils, and for the calves which he had made” (2 Chron. 11:15). With these two examples it is not surprising that in the whole land there were many high places. Hezekiah and Josiah zealously destroyed the high places, which included the buildings thereon and the idols connected therewith. The word bamah is used apparently for any idolatrous erection, for we once read of high places in a valley (Jer. 7:31).
The term “high places” has another application under the Hebrew word ramah, which also signifies “exalted”; for Israel is charged with making a high place in every street, and at every head of the way, which doubtless refers to some shrine or symbol of idolatry connected with abominable practices (Ezek. 16:24-25,31,39). They courted the favor of the heathen by adopting their idolatrous worship and customs.