In Midrash Rabbah on parshat Kedoshim (Vayikara Rabbah 25,3) it is written:
 

Rabbi Itzchak ben Rabbi Simon opened: "After HaShem your Lord you shall go" (Devarim 13:5). And is it possible for flesh and blood to go after HaShem? It is written: "Your way is in the sea and Your path is in mighty waters" and you say: after HaShem you shall go?! "And cleave to Him" – is it possible for flesh and blood to ascend to Heaven and cleave to the Shechinah? It is written "for HaShem your Lord is a consuming fire" (Devarim 4:24)… and you say "and cleave to Him?!" But (rather), from the beginning of the Creation of the world, HaShem engaged at first only in planting - this is what is written: "And HaShem planted a garden in Eden" (Bereshis 2:8) – you too, when you will enter the Land, do not engage at first except in planting. This is what is written: "when you will come into the land." (Vayikra 19:23).
 

The Midrash asks two questions, and gives one answer for both of them.
 

1. How is it possible to go after HaShem, meaning: how is it possible to reach Him, to get close to Him and to cleave to Him?

2. How is it possible to cleave to Him – and this is the same question as the first one!
 

And the answer of the Midrash: "When you will come into the Land and you will plant" – what, then is the answer? How do we cleave to HaShem by planting?

The words of Chazal are "poor" in one place and "rich" in another. The Gemara in Masechet Sotah (14a) asks the same question:

And Rabbi Hama b'Rabbi Hanina said: That which is written "after HaShem your Lord you shall go" – is it possible for a man to go after the Shechinah? Isn't it already said "for HaShem your Lord is a consuming fire"?! But rather, follow HaShem's middot (emulate His attributes) – as He clothes the naked… so you - clothe the naked. HaShem visits the sick… you too visit the sick. HaShem consoled the bereaved… you as well console the bereaved. HaShem buried the dead… so you - bury the dead.
 

Cleaving to HaShem is defined as cleaving to His attributes, His actions and derech eretz. How do we cleave to Hashem's attributes by planting? 
 

In the preface to Midrash Tanhuma on parshat Kedoshim:

"And when you will come to the Land and you will plant." HaShem said to Israel: even though you will find it full of all which is good, do not say: we will sit (idly) and not plant, but be diligent and plant, as it says: "and you shall plant all manner of trees of food." Just as you came in (to the Land) and found plants which were planted by others, so you shall plant for your children. A man should not say: I am old, how many years of life do I have, why should I exert myself for others, tomorrow I will die… if he will merit, it will be for him. If he will not merit, (it will be) for others… therefore one must not desist from planting. But just as he found, he must continue and plant, even when he is old. HaShem said to Israel: learn from Me: Do I need (that which I planted)?! As it says: "And HaShem the Lord planted a garden in Eden, to the east (Bereshis 2:8)."

This is the way to cleave to HaShem – to plant for others. Do not be concerned only for yourself, be concerned for the coming generations. Even though you will not benefit from what you are planting – others will benefit from it. This is HaShem's attribute, "the world is built upon kindness" (Tehillim 89:3) – this is the aspect of kindness in the world, upon which the world exists, and this is cleaving to HaShem, cleaving to His attributes. Planting is the basis of the world's existence by virtue of the attribute of kindness. This was the characteristic of Avraham Avinu, middat hachessed, about whom it is said: "and he planted an eshel (orchard) in Be'er Sheva" (Bereshis 21:33) – Chazal said that this eshel was Avraham's inn, where one would enter, drink and eat, and bless Hashem. Planting is the foundation of the attribute of kindness in the world.
 

In HaRav Kook's "Midrash Yerachim" on the months of the year, HaRav writes this statement in relation to the month of Shevat: "The passion for planting trees stems from the desire to benefit the generations, (and this) is most evident regarding the planting of carob (cheruv) trees."

There are three kinds (levels) of desire:
 

1. Passion (cheshek) – a simple craving for planting. There is a level higher than this:

1. Desire (ratzon) – the will and desire to plant, and to benefit from the planting. However, there is an ever higher level:


2. Wish [in the active sense] (chefetz) – the desire (wish) to benefit others.

The ideal kind of planting, says the Rav, is motivated by the desire to benefit the future generations, and this is expressed by the planting of the carob tree, which gives its fruit only after 70 years. The carob tree is the manifestation of the desire to benefit others and not being concerned for one's own benefit, as Chazal say regarding Rabbi Chanina ben Dosa: "All the world receives its sustenance for My son Chanina, and My son Chanina suffices with a kav of Carobs from Erev Shabbat to Erev Shabbat" (Chullin 86a).

However, we can see an additional dimension in the Midrash, not connected only to the individual person's cleaving to HaShem's middot, but one which also reveals that Am Israel's connection with HaShem comes through our attachment to Eretz Israel. A connection is the result of something which is shared by the ones who are connecting.
 

Eretz Israel is the point of connection between HaShem and Am Israel. HaShem's rooting and planting of Am Israel in Eretz Israel defines our connection with the Land: "Since HaShem's portion is His nation, Yaakov the lot of His inheritance" (Devarim 32:9). HaShem said: Israel, who came to be My portion, will come and inherit the Land, which came to be My portion (Midrash Tanhuma, Re'eh 8). The holiness of Eretz Israel stems from HaShem's presence specifically in this place: "The eyes of HaShem your Lord are upon it from the beginning of the year to the end of the year" (Devarim 11:12).
 

So it follows that our connecting with Eretz Israel comes about through planting, which is the expression of our taking possession of Eretz HaKodesh. This is the point of connection of Am Israel with HaShem – this is "going after HaShem" and "cleaving to Him" which stems from "when you will come into the Land and you will plant" – engage at first only in planting.