Albert Barnes Commentary Psalms 3:1

"Jehovah, how are mine adversaries increased! Many are they that rise up against me." — Psalms 3:1 (ASV)

Lord, how are they increased - How are they multiplied; or, how numerous they are. Perhaps the idea is, that at first they seemed to be comparatively few in number, but had now so multiplied as to endanger his crown and life. This is an appropriate expression on the supposition that it refers to Absalom.

At first, the number of those who adhered to Absalom was not so great as to excite much alarm. But by the arts of a demagogue, by complaining of the government, and by saying that if he were made a judge in the land, every man would have justice done him (2 Samuel 15:4–5), he won the hearts of the people and gathered so many under his standard that it became necessary for the king to flee from Jerusalem to a place of safety.

That trouble me - literally, my enemies. The allusion is to those who were now enlisted under Absalom and who were engaged in endeavoring to overthrow the government.

Many are they that rise up against me - That is, those who have become my enemies.