"Every priest stands daily ministering and offering time after time the same sacrifices, which can never take away sins; but He, having offered one sacrifice for sins for all time, sat down at the right hand of God" (Hebrews 10:11-12).
Throughout this book, the Hebrew writer has been demonstrating why Jesus Christ and His new covenant are better than the system put in place by God through Moses. The above passage continues in this theme. It contrasts the work of the Levitical priests and the work of Christ.
The contrast is a simple one. The priests of old stand daily. Jesus sat down.
The implication is that the priests stand daily because their work was never done. Every time they offered a sacrifice, they would later have to offer another. And these sacrifices themselves would never atone for sins.
On the other hand, Jesus sat down. His work of sacrificing is done. He offered one perfect sacrifice, His life. He will never have to offer His life again, because the first offering was fully sufficient.
The lesson for the Hebrews was for them not go back to the old system. Atonement for sins and salvation is in Christ. If they deserted Him, they had no hope.
Today, there are probably not many Christians tempted to go back to Judaism. But the basic point still applies. Salvation is found only in Christ. If we desert Him, we will be lost. Let us remain faithful and devote our lives to the One who offered His life on the cross for us.