What is the significance of 'I will build my church' being in the future tense?
The future tense indicates that the church would be built after Jesus spoke, and its foundation is Christ Himself—the only rock of Scripture—not Peter. It points to a future work tied to His death, burial, and resurrection, which believers appropriate by faith.
Les teaches that Jesus' words 'upon this rock' use the term rock symbolically. The rock is not Peter but Christ, the only rock of Scripture. The future tense—'I will build'—shows the building of the church was still future and would be built upon Christ Himself. Les then points back to Exodus 17, where the rock was smitten, as a great lesson. For believers on this side of the work of the cross, that work means His death, burial, and resurrection, and it is appropriated by faith.
And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it.