God continually shows us in nature that there will be a resurrection

Let us consider, beloved, how the Lord continually proves to us that there shall be a future resurrection, of which He has rendered the Lord Jesus Christ the first-fruits by raising Him from the dead. Let us contemplate, beloved, the resurrection which is at all times taking place. Day and night declare to us a resurrection. The night sinks to sleep, and the day arises; the day [again] departs, and the night comes on. Let us behold the fruits [of the earth], how the sowing of grain takes place. The sower goes forth, and casts it into the ground; and the seed being thus scattered, though dry and naked when it fell upon the earth, is gradually dissolved. Then out of its dissolution the mighty power of the providence of the Lord raises it up again, and from one seed many arise and bring forth fruit.

Taken from Chap. XXIV. of the first epistle of Clement to the Corinthians. From "The Early Church Fathers and Other Works" originally published by Wm. B. Eerdmans Pub. Co. in English in Edinburgh, Scotland beginning in 1867. (ANF 1, Roberts and Donaldson). The digital version is by The Electronic Bible Society, P.O. Box 701356, Dallas, TX 75370, 214-407-WORD.