Even if a principle from the OT is referenced in the NT, that doesn't necessarily mean it's intended for Christian instruction.
"By faith Abraham, when he was tested, offered up Isaac, and he who had received the promises offered up his only begotten son,"—Hebrews 11:17
Maybe now we should think about offering child sacrifices. The message in this passage is faith, not child sacrifice.
"By faith he kept the Passover and the sprinkling of blood, lest he who destroyed the firstborn should touch them."—Hebrews 11:28
Maybe we should all keep the Passover and apply lamb's blood to our doorposts. Likewise, this also is about faith, not keeping the Passover.
The passage in Hebrews 7 isn't about Christians giving a tenth. It's about the superiority of Christ's priesthood over the Levitical priesthood.