Rock.
Two words are principally employed for this word. One is sela, 'an elevation of strength, immovable': used symbolically for Jehovah as the rock of His people: "Jehovah is my rock and my fortress." Psalms 18:2. He hath "set my feet upon a rock, and established my goings." Psalms 40:2.
The other word is tsur, a rock, generally sharp and precipitous, 'a place of shelter and security': "Lead me to the rock that is higher than I"; Thou art "my father, my God, and the rock of my salvation." "My God is the rock of my refuge." Psalms 61:2; Psalms 89:26; Psalms 94:22.
In the N.T. any one who heard and did the sayings of the Lord is compared to a man who built his house upon the rock which nothing could shake. Matthew 7:24, Matthew 1:7; Luke 6:48. The Lord said, "Thou art Peter [petros], and upon this rock [petra] I will build my church." The church is being built upon what Peter confessed, Christ Himself, the Son of the living God. Matthew 16:16-18: cf. 1 Corinthians 3:11; 1 Corinthians 1:10.