Love of God is yearning for Him. One’s soul is a spiritual rather than material entity. Therefore, it yearns for that from which it benefits and which brings it strength. Love of God encompasses all areas of life. One who loves God will continue to serve Him and trust in Him even when it is difficult.

Love of God is the soul being drawn toward God:

But what is the love of God? It is the yearning of the soul, its inclination toward the Creator so that it can connect to His supernal light.

The soul is connected to God and is distinct from the body:

That is, the soul is an immaterial, spiritual entity. It is inclined toward that which is similar to it, i.e., spiritual beings, and naturally distances itself from that which is opposite to it, i.e., physical entities. The Creator tied the soul to this coarse, unclean body that is full of darkness, because He wanted to test the soul in its control of the body. Accordingly, He roused it to have compassion on the body and to bring benefit to it for the good of the partnership and connection that was generated between them from the outset.

The soul is drawn toward that which gives it light and strength:

When the soul senses something that is of use to the body and advantageous to its constitution, it will be inclined toward it and desire it, seeking rest from the afflictions and ailments of the body. This is like a person who desires an expert doctor when he is sick, so that he has someone to attend to him and think about him. When the soul senses something that adds light and strength to its essence, it thinks of that thing, clings to the idea of it, and considers and desires it. This is pure love.

The actions of one who loves:

Then the soul will drink from the cup of love of God, and will enjoy the bliss of being alone with God, devoting itself wholeheartedly to Him, loving Him, putting its trust in Him, and yearning for Him. It will have no other occupation than His service, and no ideas or thoughts other than of Him. It will not move any of the limbs of its body except to perform actions which will gain His favor. It will not unbind its tongue except to refer to Him, praise Him, thank Him, and laud Him out of love for Him and out of longing to do His will. If He bestows a benefit on the soul, it will thank Him. If He brings suffering on it, it will patiently bear it, and will only increase its love for Him and trust in Him. (Rabbeinu Baĥya ibn Pekuda, Ĥovot HaLevavot 10:1)

Further reading: For more on the human soul, see p. 218.

Love makes a person do things without receiving any reward, acting in accordance with the truth purely because it is the truth. When a person loves God, he performs the mitzvot out of love for Him. Great love accompanies one always, and one who loves God thinks only of Him.

Serving God out of love means acting in accordance with the truth purely because it is the truth:

One who serves out of love engages in Torah and mitzvot and walks in the paths of wisdom, not because of anything in the world, nor because of fear of misfortune, nor in order to acquire benefit; rather, he acts in accordance with the truth because it is the truth, and in the end, benefit will come as a result.

The level of one who serves God out of love:

This level is a very high level, and not every wise person attains it. It is the level of our patriarch Abraham, whom the Holy One, blessed be He, referred to as the one who loves Him (Isaiah 41:8), because he served God only out of love. This is the level with regard to which the Holy One, blessed be He, commanded us through Moses, “You shall love the Lord your God” (Deuteronomy 6:5). When one loves God with proper love, he will immediately perform all the mitzvot out of love.

What is proper love?

What is proper love? One must love God with great, exceedingly strong love, such that his soul is tied up with love of God. He should think of it always, like one who is lovesick, whose mind is never free from his love for a certain woman, and who is always preoccupied with her, whether he is sitting, standing, or eating and drinking. Love of God, in the hearts of those who love Him, is even greater. They think of it always, as He commanded us to, “with all your heart, and with all your soul” (Deuteronomy 6:5). This is what Solomon referred to by way of an analogy: “For I am lovesick” (Song of Songs 2:5), and all of Song of Songs [which describes the love between a man and a woman] is an allegory for this matter. (Rambam, Mishneh Torah, Hilkhot Teshuva 10:2–3)