There have been some questions about typology and its justification as a form of scriptural interpretation. I would make several points:
1. The NT deals with the OT in a typological fashion. We must follow God's Word as to how God's Word is to be read.
2. If God throughout salvation history is the same God who reveals himself in Jesus Christ, then his former actions must be analogically similar to his later actions- since it's the sameGod, witht he same character, right? Consequently, typological interpretation of Scripture makes perfect sense if you believe God to be the author of Scripture and salvation history.
3. God's activity in the OT is the story of his life in solidarity with Israel through the binding of the different covenants. God always directed these covenants and his activity in relationship to them to there ultimate fulfillment in Jesus. Jesus is the surpreme representation of God and Israel bound together in covenant, in that he is both God and man come together not only in the unity of covenant, but in personal union. Therefore, all of God's previous actions in both creation and redemption must be read in light of Christ and pointing to Christ both in the form of rectilinear prophecy, but also in a typological fashion in that God's previous saving actions echoe their fulfillment in Christ.
4. Therefore, if we reject typological interpretation, we automatically fall into Marcionism. There is no other option.