Reaching ahavas Yisrael through preparatory mitzvos

וכל אלה הדברים בפסוק קדושים תהיו ואהבת לרעך כמוך ויראת מאלהיך הם ג"כ הבטחות כי ע"י שמירת אלה המצות יזכו לאלה המדרגות.

And all these statements in the pasuk — "You shall be holy," "You shall love your fellow as yourself," "and you shall fear your God" — are also promises, for through keeping these mitzvos one will merit to reach these very levels.

The Sefas Emes reads these commands not only as demands but as guarantees: the very acts of the mitzvos lift a person into the lofty states of kedushah, love, and yiras Shomayim that the words name.

כאשר חכמים הגידו כי ואהבת לרעך כלל גדול בתורה א"כ קשה מאוד לקיימה רק באמצעיות מצות הקודמות ל"ת רכיל.

As Chazal taught, that "You shall love your fellow as yourself" is a great principle of the Torah — therefore it is very hard to fulfill, except by means of the mitzvos that precede it: "Do not go as a talebearer."

Because loving one's fellow is so all-encompassing, it cannot be reached directly; it must be built up through the earlier, more practical mitzvos that clear away gossip and ill will (Rashi, Vayikra 19:18).

לא תשנא.

"Do not hate."

First a person must uproot hatred from his heart — a necessary step on the way to genuine love.

הוכח.

"You shall surely rebuke."

Offering honest, caring tochachah (rebuke) to one's fellow is itself an expression of love and a rung on the ladder toward it.

זוכין אח"כ לואהבת כנ"ל:

One then merits to reach "You shall love" — as explained above.

Only after removing talebearing, hatred, and indifference does the heart become capable of the great mitzvah of loving one's fellow as oneself.

Summary: The commands to be holy, to love one's fellow, and to fear Hashem are also promises of the levels they describe. Because "love your fellow" is the great principle of the Torah, it cannot be attained directly — it is reached only through the preparatory mitzvos of refraining from gossip and hatred and offering proper rebuke.