5 “Moses was faithful as a servant in all God’s house,”a bearing witness to what would be spoken by God in the future.

Read Hebrews 3:5 Using Other Translations

And Moses verily was faithful in all his house, as a servant, for a testimony of those things which were to be spoken after;
Now Moses was faithful in all God's house as a servant, to testify to the things that were to be spoken later,
Moses was certainly faithful in God’s house as a servant. His work was an illustration of the truths God would reveal later.