Ecclesiastes 3:15.

Somebody please tell me what this means. I've searched for commentaries all over the internet and couldnt find nothing but the verse or commentaries I couldn't understand. Thankyou

(Ecc 1:9) The thing that hath been, it is that which shall be; and that which is done is that which shall be done: and there is no new thing under the sun.

i think that.

It means that time is not as solid and linear as one might think.

There are many verses that defy our notion of time:
John 5:25 Verily, verily, I say unto you, The hour is coming, and now is, when the dead shall hear the voice of the Son of God: and they that hear shall live.

John 4:23 But the hour cometh, and now is, when the true worshippers shall worship the Father in spirit and in truth: for the Father seeketh such to worship him.

There are also things that exist even though they never existed at all:
Revelation 17:8 The beast that thou sawest was, and is not; and shall ascend out of the bottomless pit, and go into perdition: and they that dwell on the earth shall wonder, whose names were not written in the book of life from the foundation of the world, when they behold the beast that was, and is not, and yet is.

There are also things that happened to you that you don't remember:
Ephesians 2:6 And hath raised us up together, and made us sit together in heavenly places in Christ Jesus:

Jesus the Lamb of God died for our sins and was raised 2000 years ago.
But the Lamb of God (Jesus )was actually slain from the foundation of the world.
So we were actually raised and seated with Christ before the foundation of the world.
The Holy Spirit will bring all things to our memory so if your experiencing memories that are not yours(as far as you know) don't sweat it.In God time and matter don't matter all the time.