When we look at an object, we don't really see that object. What we actually see is light waves bouncing off that object. Our brains analyze the light that our eyes gather and we see the object. Without the light bouncing off the object, we can't see the object! In a totally dark room devoid of any light whatsoever, we can't see anything, although the room may be full of things. Have you ever walked through your bedroom late at night, maybe to answer the phone, and stump your toe on a table leg? Why did that happen? It happened because you couldn't see the table in the dark. The table was just as much there as it was in the daylight, but in the dark, with no light to bounce off it into your eyes, it was invisible!
The Bible tells us that faith "is the substance of things hoped for, the evidence of things not seen". Faith gives substance to things we can't see. Faith allows us to see what we have hoped for! Faith is to spiritual eyes what light is to physical eyes! Without faith, we can't see the "spiritual blessings in heavenly places" that God has given to us. But, just like the table leg in the dark, just because we can't see them doesn't mean that they're not there! Faith gives us the ability to see spiritual things.
Now, someone might say that the Bible is talking about spiritual blessings, not physical blessings. Well, God is a spiritual being. He gives spiritual blessings. But we must remember that since God created everything out of nothing, everything was at one time spiritual! God spoke the trees into being, they were not made of anything that existed before, they were created out of spirit! Since everything was created out of spiritual material, everything was at the beginning, a spiritual blessing!
The only way to make a "spiritual blessing in heavenly places" a material blessing here on Earth, is to acquire it by faith! Faith gives substance to the things we hope for, the things God gives us "according to His riches in Heaven, in Christ Jesus"! God is a spirit and Heaven is a spiritual place and everything there is spiritual. And so we can be sure that God's "riches in Heaven" are spiritual as well. But, when a spiritual blessing gains substance, it is no longer spiritual, but material! Just like the light allows us to see material things, faith allows us to see spiritual things!