God's covenant with David is fulfilled through Jesus. God will always do what He says. All the promises of God are fulfilled in Jesus.
The cracks in Saul's life become visible. His foundation is shaky. His kingdom will not endure because his heart is not perfect toward God.
The last thing Jesus does with His disciples is to pray for them. What does Jesus pray about? What is on His heart as He is about to leave them?
King Saul was challenged to lay a firm foundation for his kingdom. Would he fear God and obey His Word? Will we lay this firm foundation in our lives?
Jesus' work didn't end at the cross. It continues because Jesus lives. He reminds His disciples in John 16 that He will see them again. We serve a risen Savior.