I wonder if there are any scriptural references or slokas that tell us why the fruits of our actions are faced by us in our next life as any jiva or as a human, and why not in this life itself?
It is not necessary that the we will have to wait till the next life. But it takes time. And, mostly, the time taken is greater than one lifetime.
This can be understood if we visualize our Karmas in the form of tree that bears fruits.
Lord Shiva says the following:
DAridrya-dukkha-rogAshcha vandhana-vyAsanAni cha |
AtmAparAdha-vrikshasya phalAn-yetAni dehinAm ||
Poverty, misery, diseases, bondage and the bad habits -- these all are the fruits of the tree (Atma-Aparadha Vriksha) which is the manifestation of the Jiva's misdeeds.
KulArnava Tantram 1.54
Now, if we visualize our performing of the Karma as sowing of seed in the soil, then it takes a lot of time for the seed to grow into a fruit-bearing tree. And, these fruits are what we call Karmaphala.
Just like the fruits are not obtained immediately after the seed is sown, the Karmaphala is analogously not immediately experienced by the Jiva.
So, it is guaranteed that there will be a gap of time between the instance an action is performed and the instance when it's fruits are ready to be experienced.
But, it is really difficult to say how long this gap will be.