Jesus was talking to the Jews here, His chosen people. At that time, they were still under the Law, because Jesus had not yet been crucified, and arisen. Here's a passage to "chew" on:
Jeremiah 31:31 Behold, the days come, saith the Lord, that I will make a new covenant with the house of Israel, and with the house of Judah:
32 Not according to the covenant that I made with their fathers in the day that I took them by the hand to bring them out of the land of Egypt; which my covenant they brake, although I was an husband unto them, saith the Lord:
33 But this shall be the covenant that I will make with the house of Israel; After those days, saith the Lord, I will put my law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people.
Under the Law, man could break it because it was "works based", and if they didn't follow it, they were goners.
Hebrews 8:7 For if that first covenant had been faultless, then should no place have been sought for the second.
8 For finding fault with them, he saith, Behold, the days come, saith the Lord, when I will make a new covenant with the house of Israel and with the house of Judah:
9 Not according to the covenant that I made with their fathers in the day when I took them by the hand to lead them out of the land of Egypt; because they continued not in my covenant, and I regarded them not, saith the Lord.
10 For this is the covenant that I will make with the house of Israel after those days, saith the Lord; I will put my laws into their mind, and write them in their hearts: and I will be to them a God, and they shall be to me a people:
Hebrews 10:16 This is the covenant that I will make with them after those days, saith the Lord, I will put my laws into their hearts, and in their minds will I write them;
17 And their sins and iniquities will I remember no more.
Under the Law, their sins were remembered every year, that is why the High Priest would enter into the innermost part of the tabernacle, to make a once a year atonement. Jesus fulfilled this, and He is now our High Priest.
We are now under the Grace Covenant now. We can not, and will not, break this covenant betwixt God and us.