Hebrews 2:1-3
So [then], we [Christians] should pay closer attention to the things we have heard, so that we do not drift away from [believing and practicing] them.
Hebrews 10:28-29
The person who has disregarded the law of Moses is put to death without being shown mercy on the testimony of two or three witnesses.
Hebrews 12:25
Pay careful attention so that you do not refuse [to hear] God when He speaks to you. [See verse 9]. For if those people [i.e., the Israelites] did not escape [judgment] when they refused [to hear] Him who warned them on earth [i.e., God speaking through Moses at Mount Sinai], how much less [likely] will we escape [judgment] if we reject Him who warns from heaven [i.e., Christ]?