In times past God spoke to our forefathers through the prophets in many parts and in various ways,

For it was fitting that God, for whom and through whom everything exists, in order to lead many [of His] children to glory [i.e., heaven], would make the author [or, pioneer] of their salvation [i.e., Jesus] completely [qualified] through [His] sufferings.

[Now] we have many things to say about Melchizedek, but because of your slowness to grasp things, they are hard to explain.

And on one hand, many people were appointed to be [Levitical] priests because they were prevented by death from continuing [to serve]. [Note: The idea is that Levitical priests had to be constantly replaced].

so Christ also, who was once [for all] offered [as a sacrifice] to take away the sins of many people, will come back a second time, not to take away sin, [but] to provide salvation to those who are waiting for Him.

By [having] faith, when Abraham was tested [by God], he offered Isaac [as a sacrifice]. [Even though] he had received the promises [of having many descendants], he was ready to offer his only conceived [and eventually born] son,

Look carefully [at how you are living] so that no one falls away from God's unearned favor, and that no "poisonous plant sprouts up" to cause trouble and corrupt many people [Note: This is an analogy from Deut. 29:16-18 being used as a warning against the evil influence of wicked people],