In Judges 13 we are introduced to Samson's parents, Manoah and an unnamed woman. In Judges 14 we are introduced to Samson and his bride (who also goes unnamed. Did you know he was married before he met Delilah?).
Samson spots a woman in Timnah and decides she's "the one". He insists his parents arrange their marriage, even though she was a Philistine. This was all part of God's plan, as foretold by the angel in Chapter 13 - that Samson would "begin the deliverance of Israel from the hands of the Philistines." Does it seem strange that Samson marries a Philistine in order to deliver his people from the Philistines?
It is good to know that God is sovereign in all things. We don't need to know or understand His plan, we just need to submit to the power of the Spirit.