It is "His house-whose house we are" (Heb 3:6). But there is a contingency because the next phrase starts with "if." "If we hold fast our confidence and the boast of our hope firm until the end" (:6). There is a parallel regarding the sower of seed where some "'fell on the rocky ground . . . [but] it had no depth of soil'" (Mk 4:5). It represents people who "'when they hear the word immediately receive it with joy; and they have no firm root in themselves, but are only temporary; then when affliction or persecution arises because of the word, immediately they fall away'" (:16-17). If they receive the word joyfully you would assume it had been understood. "But a natural man does not accept the things of the Spirit of God, for they are foolishness to him; and he cannot understand them, because they are spiritually appraised" (1Co 2:14). However, it is predicated on whether they have a "'firm root in themselves'" (Mk 4:16). You are motivated "'with all your heart, and with all your soul, and with all your mind'" (Mt 22:37). It is more than just your mind saying to itself that something is true. If that was the only criteria then if you drink in this way you "'will thirst again'" (Jn 4:13). "'Whoever wishes to save his life will lose it; but whoever loses his life for My sake will find it'" (Mt 16:25). He who "'drinks My blood has eternal life, and I will raise him up on the last day'" (6:54). They are to then hold on to it firmly "'until the end'" (:6). But for these it is only "'temporary'" (:17) and they "'fall away'" (:17) which is defined as apostasy.