[1] Now faith is the grounds (substance, assurance) of things, which are hoped for, and the evidence (proving) of things which are not seen.
Hebrews 11:1 GNV
[6] But without faith it is unpossible to please him: for he that cometh to God, must believe that God is, and that he is a rewarder of them that seek him.
Hebrews 11:6 GNV
So many powerful examples here. For each and everyone listed here there was a "now", and they were looking forward to a “then”. Their faith caused them to act on the promise which they had now looking for that promise yet to be fulfilled then. Even Enoch in his faith did not experience bodily death, God simply translated him, God took him undead to be with Him. Noah did not believe in the ark. He built an ark by faith, that is faith in God, taking Him at His word. He received life itself by entering the ark in his NOW, but his was only an example of a future promise of life
But what is said of all these like Noah is:
[13] All these died in faith, and received not the promises, but saw them a far off, and believed them, and received them thankefully, and confessed that they were strangers and pilgrims on the earth.
Hebrews 11:13 GNV
[16] But now they desire a better, that is an heavenly: wherefore God is not ashamed of them to be called their God: for he hath prepared for them a city.
Hebrews 11:16 GNV
Jesus also gave an example of Now and Then.
[14] And as Moses lift up the serpent in the wilderness, so must that Son of man be lift up, [15] That whosoever believeth in him, should not perish, but have eternal life. [16] For God so loved the world, that he hath given his only begotten Son, that whosoever believeth in him, should not perish, but have everlasting life.
John 3:14-16 GNV
When that serpent was lifted up we are told that the people being bitten by fiery serpents only had to look and they would live. That happened in their NOW right there immediately at that time. And Jesus told Nicodemus right there in his NOW that whosoever believeth in Him should not perish, but have everlasting life NOW, in the present then And what he had in his NOW was that assurance of what he would have THEN. Just hold on to that thought.
From that time in Numbers 2 when fiery serpents came among the people God instructed Moses to make a brasen serpent. God's intent and desire was for the people to simply obey His word, "Look, and live". And as a reminder the children of Israel kept that reminder around for awhile, literally hundreds of years. In 2 Kings 18 we read that Hezekiah broke that brazen serpent Moses had made because the children of Israel were burning incense to it.
In much the same way, but even with greater strength and emphasis Jesus told Nicodemus that the Son of man must be lifted up that whosoever believes in Him NOW has eternal life NOW. Jesus clarified this for Nicodemus to understand right then and there:
[17] For God sent not his Son into the world, that he should condemn the world, but that the world through him might be saved. [18] He that believeth in him, is not condemned: but he that believeth not, is condemned already, because he hath not believed in the Name of that only begotten Son of God.
John 3:17-18 GNV
The believing in the only begotten Son of God unto everlasting life takes place when that person is alive here on earth in each person's NOW, not waiting until that future judgment day that is coming. And that believing not is also here on earth in each person's NOW, and they are condemned already because they have not believed in the Name of the only begotten Son of God. As Jesus taught about the wheat and the tares (Matthew 13) they are left to grow in this world NOW until the end of the age when the judgment takes place THEN. Just like at the beginning the thought of faith being the assurance of things hoped for, having hope in the Son of man lifted up in eternal life NOW, the proving of things not (yet) seen, eternal life THEN in that great judgment day.
Faith, believing in Jesus NOW gives eternal life NOW, and the hope in the promise of eternal life THEN. It is hope in an assured and proven truth.
And just the same not believing in the Name of the only begotten Son of God NOW is condemned already NOW, and as they will be also in that great judgment day THEN.