Concise Bible Dictionary:
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” (Psa. 18:2). He hath “set my feet upon a rock, and established my goings” (Psa. 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” (Psa. 61:2; Psa. 89:26; Psa. 94:22).
In the New Testament anyone 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 (Matt. 7:24-25; Luke 6:48). The Lord said, “Thou art Peter (πέτρος), and upon this rock (πέτρα) I will build My church.” The church is being built upon what Peter confessed, Christ Himself, the Son of the living God (Matt. 16:16-18; compare 1 Cor. 3:11; 1 Cor. 10:4).