Genesis 7:2-3 – Noah takes 7 pairs of animals onto the ark
Genesis 6:19 – Noah only takes one pair of animals onto the ark
From just a cursory look at those sections of Scripture we could conclude that there is an obvious discrepency, and that not only in what Noah did but also in what God told him to do. One place mentions that one pair of animals of each kind was to be taken into the ark, the other place however speaks of 7 pairs of animals each to be taken into the ark. What's the solution to this apparent difficulty? The discrepency can be solved when we read carefully what the verses actually state.
Gen 6:19 states, "And of every living thing of all flesh, two of every sort shalt thou bring into the ark, to keep them alive with thee; they shall be male and female." Here we have God's instruction to Noah, that he was to bring one pair of "every living thing of all flesh" into the ark, and the purpose for that is said to have been "to keep them alive with thee" and therefore, "they shall be male and female". We learn that of all kinds of animals, Noah was to bring one pair, one male and one female, into the ark to ensure that they could multiply and continue to live later on. This included land animals as well as fowl of the air (cp. 6:20).
Gen 7:2-3 state, "Of every clean beast thou shalt take to thee by sevens, the male and his female: and of beasts that are not clean by two, the male and his female. Of fowls also of the air by sevens, the male and the female; to keep seed alive upon the face of all the earth." There is an important distinction made here, because Noah was here instructed not concerning "every anmial", but solely concerning "every CLEAN beast …" This instruction concerned only clean animals, and it simply was in addition to the previous mention of taking one pair for the purpose of keeping them alive. The additional pairs of only the clean animals were obviously taken along for a different purpose, because only one pair was sufficient and served the purpose to provide a means for to keep them alive. The purpose for seven pairs of the clean animals becomes clear later on when we read of Noh making sacrifices right after the flood, for had he not taken extra pairs of the clean animals he could not have made sacrifices to the LORD and at the same time kept those kinds of animals alive.
We therefore do not have a contradiction here, but rather see how there is one more general instruction concerning all animals for the purpose of keeping them alive, and then there is an additional instruction concerning only clean animals in order to provide for sacrifces and still keeping those kinds of animals alive.