Things not seen, are realities that are here and now. It may also refer to past realities, in v.3 the Bible says: "Through faith we understand that the worlds were framed by the word of God, so that things which are seen were not made of things which do appear." The Creation account happened and we know this is true because God told us so, and very plainly in His Word (Gen. 1). Faith completely believes God even in the face of fickle science. There are spiritual realities that are present with us even though we may not physically see them. We cannot see how God forgives sins, but we know, through faith that if we confess and forsake our sins, He is faithful and just to forgive us our sins. We may not see how Jesus Christ intercedes for us, but we know that He does because the Bible says so. We may not necessarily see it, but we know that every spiritual blessing comes from God and that He daily loadeth us with benefits, why because the Bible said so. Jesus proclaims a blessing to those who believe on Him despite not having seen Him (John 20:29). The Bible is full of things not seen. And faith relates to those things, by forming within, or that faith itself becomes to us a certain conviction of matters not seen. We need not see it to believe it, rather we read it and believe it. That is we read it in God's Word, and we know we can believe it to be true.