John Gill Commentary 1 Samuel 20:22

"But if I say thus unto the boy, Behold, the arrows are beyond thee; go thy way; for Jehovah hath sent thee away." — 1 Samuel 20:22 (ASV)

But if I say thus to the young man, behold, the arrows [are]
beyond you
Being shot to a greater distance than where the young man was:

go your way, for the Lord has sent you away ;
then he was to depart directly, without staying to have any conversation with Jonathan, which would not be safe for either of them, and so make the best of his way into the country, and escape for his life;

For so it was ordered by the providence of God, that he must not stay, but be gone immediately: the signals were these, that if things were favourable, then he would shoot his arrows on one side of the lad, and David might come out and show himself at once; but if not, he would shoot them beyond him, by which he might know that he must flee for his life.